Default value of pcc_subspace_idx is -1.
Make sure to check pcc_subspace_idx before using the same as array index.
This will avoid following KASAN warnings too.

[   15.113449] ==================================================================
[   15.116983] BUG: KASAN: global-out-of-bounds in cppc_get_perf_caps+0xf3/0x3b0
[   15.116983] Read of size 8 at addr ffffffffb9a5c0d8 by task swapper/0/1
[   15.116983] CPU: 3 PID: 1 Comm: swapper/0 Not tainted 4.15.0-rc2+ #2
[   15.116983] Hardware name: Dell Inc. OptiPlex 7040/0Y7WYT, BIOS 1.2.8 01/26/2016
[   15.116983] Call Trace:
[   15.116983]  dump_stack+0x7c/0xbb
[   15.116983]  print_address_description+0x1df/0x290
[   15.116983]  kasan_report+0x28a/0x370
[   15.116983]  ? cppc_get_perf_caps+0xf3/0x3b0
[   15.116983]  cppc_get_perf_caps+0xf3/0x3b0
[   15.116983]  ? cpc_read+0x210/0x210
[   15.116983]  ? __rdmsr_on_cpu+0x90/0x90
[   15.116983]  ? rdmsrl_on_cpu+0xa9/0xe0
[   15.116983]  ? rdmsr_on_cpu+0x100/0x100
[   15.116983]  ? wrmsrl_on_cpu+0x9c/0xd0
[   15.116983]  ? wrmsrl_on_cpu+0x9c/0xd0
[   15.116983]  ? wrmsr_on_cpu+0xe0/0xe0
[   15.116983]  __intel_pstate_cpu_init.part.16+0x3a2/0x530
[   15.116983]  ? intel_pstate_init_cpu+0x197/0x390
[   15.116983]  ? show_no_turbo+0xe0/0xe0
[   15.116983]  ? __lockdep_init_map+0xa0/0x290
[   15.116983]  intel_pstate_cpu_init+0x30/0x60
[   15.116983]  cpufreq_online+0x155/0xac0
[   15.116983]  cpufreq_add_dev+0x9b/0xb0
[   15.116983]  subsys_interface_register+0x1ae/0x290
[   15.116983]  ? bus_unregister_notifier+0x40/0x40
[   15.116983]  ? mark_held_locks+0x83/0xb0
[   15.116983]  ? _raw_write_unlock_irqrestore+0x32/0x60
[   15.116983]  ? intel_pstate_setup+0xc/0x104
[   15.116983]  ? intel_pstate_setup+0xc/0x104
[   15.116983]  ? cpufreq_register_driver+0x1ce/0x2b0
[   15.116983]  cpufreq_register_driver+0x1ce/0x2b0
[   15.116983]  ? intel_pstate_setup+0x104/0x104
[   15.116983]  intel_pstate_register_driver+0x3a/0xa0
[   15.116983]  intel_pstate_init+0x3c4/0x434
[   15.116983]  ? intel_pstate_setup+0x104/0x104
[   15.116983]  ? intel_pstate_setup+0x104/0x104
[   15.116983]  do_one_initcall+0x9c/0x206
[   15.116983]  ? parameq+0xa0/0xa0
[   15.116983]  ? initcall_blacklisted+0x150/0x150
[   15.116983]  ? lock_downgrade+0x2c0/0x2c0
[   15.116983]  kernel_init_freeable+0x327/0x3f0
[   15.116983]  ? start_kernel+0x612/0x612
[   15.116983]  ? _raw_spin_unlock_irq+0x29/0x40
[   15.116983]  ? finish_task_switch+0xdd/0x320
[   15.116983]  ? finish_task_switch+0x8e/0x320
[   15.116983]  ? rest_init+0xd0/0xd0
[   15.116983]  kernel_init+0xf/0x11a
[   15.116983]  ? rest_init+0xd0/0xd0
[   15.116983]  ret_from_fork+0x24/0x30

[   15.116983] The buggy address belongs to the variable:
[   15.116983]  __key.36299+0x38/0x40

[   15.116983] Memory state around the buggy address:
[   15.116983]  ffffffffb9a5bf80: fa fa fa fa 00 fa fa fa fa fa fa fa 00 fa fa fa
[   15.116983]  ffffffffb9a5c000: fa fa fa fa 00 fa fa fa fa fa fa fa 00 fa fa fa
[   15.116983] >ffffffffb9a5c080: fa fa fa fa 00 fa fa fa fa fa fa fa 00 00 00 00
[   15.116983]                                                     ^
[   15.116983]  ffffffffb9a5c100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   15.116983]  ffffffffb9a5c180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
[   15.116983] ==================================================================

Fixes: 85b1407b (ACPI / CPPC: Make CPPC ACPI driver aware of PCC subspace IDs)
Reported-by: Changbin Du <changbin.du@intel.com>
Signed-off-by: George Cherian <george.cherian@cavium.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>