If a CPU is offline during the driver init, we could end up causing
a kernel crash trying to register the coresight device for the TRBE
instance. The trbe_cpudata for the TRBE instance is initialized only
when it is probed. Otherwise, we could end up dereferencing a NULL
cpudata->drvdata.

e.g:

[    0.149999] coresight ete0: CPU0: ete v1.1 initialized
[    0.149999] coresight-etm4x ete_1: ETM arch init failed
[    0.149999] coresight-etm4x: probe of ete_1 failed with error -22
[    0.150085] Unable to handle kernel NULL pointer dereference at virtual address 0000000000000050
[    0.150085] Mem abort info:
[    0.150085]   ESR = 0x96000005
[    0.150085]   EC = 0x25: DABT (current EL), IL = 32 bits
[    0.150085]   SET = 0, FnV = 0
[    0.150085]   EA = 0, S1PTW = 0
[    0.150085] Data abort info:
[    0.150085]   ISV = 0, ISS = 0x00000005
[    0.150085]   CM = 0, WnR = 0
[    0.150085] [0000000000000050] user address but active_mm is swapper
[    0.150085] Internal error: Oops: 96000005 [#1] PREEMPT SMP
[    0.150085] Modules linked in:
[    0.150085] Hardware name: FVP Base RevC (DT)
[    0.150085] pstate: 00800009 (nzcv daif -PAN +UAO -TCO BTYPE=--)
[    0.150155] pc : arm_trbe_register_coresight_cpu+0x74/0x144
[    0.150155] lr : arm_trbe_register_coresight_cpu+0x48/0x144
  ...

[    0.150237] Call trace:
[    0.150237]  arm_trbe_register_coresight_cpu+0x74/0x144
[    0.150237]  arm_trbe_device_probe+0x1c0/0x2d8
[    0.150259]  platform_drv_probe+0x94/0xbc
[    0.150259]  really_probe+0x1bc/0x4a8
[    0.150266]  driver_probe_device+0x7c/0xb8
[    0.150266]  device_driver_attach+0x6c/0xac
[    0.150266]  __driver_attach+0xc4/0x148
[    0.150266]  bus_for_each_dev+0x7c/0xc8
[    0.150266]  driver_attach+0x24/0x30
[    0.150266]  bus_add_driver+0x100/0x1e0
[    0.150266]  driver_register+0x78/0x110
[    0.150266]  __platform_driver_register+0x44/0x50
[    0.150266]  arm_trbe_init+0x28/0x84
[    0.150266]  do_one_initcall+0x94/0x2bc
[    0.150266]  do_initcall_level+0xa4/0x158
[    0.150266]  do_initcalls+0x54/0x94
[    0.150319]  do_basic_setup+0x24/0x30
[    0.150319]  kernel_init_freeable+0xe8/0x14c
[    0.150319]  kernel_init+0x14/0x18c
[    0.150319]  ret_from_fork+0x10/0x30
[    0.150319] Code: f94012c8 b0004ce2 9134a442 52819801 (f9402917)
[    0.150319] ---[ end trace d23e0cfe5098535e ]---
[    0.150346] Kernel panic - not syncing: Attempted to kill init! exitcode=0x0000000b

Fix this by skipping the step, if we are unable to probe the CPU.

Fixes: 3fbf7f01 ("coresight: sink: Add TRBE driver")
Reported-by: Bransilav Rankov <branislav.rankov@arm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: stable <stable@vger.kernel.org>
Tested-by: Branislav Rankov <branislav.rankov@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Link: https://lore.kernel.org/r/20211014142238.2221248-1-suzuki.poulose@arm.comSigned-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>