pxa_timer wants to be able to call clk_enable() etc on this clock,
but our clk_enable() implementation expects non-NULL enable/disable
operations.  Provide these dummy implementations.

Unable to handle kernel NULL pointer dereference at virtual address 00000000
pgd = c0204000
[00000000] *pgd=00000000
Internal error: Oops: 80000005 [#1] ARM
Modules linked in:
CPU: 0 PID: 0 Comm: swapper Not tainted 4.8.0-rc2+ #887
Hardware name: Intel-Assabet
task: c0644590 task.stack: c0640000
PC is at 0x0
LR is at clk_enable+0x40/0x58
pc : [<00000000>]    lr : [<c021b178>]    psr: 600000d3
sp : c0641f60  ip : c0641f4c  fp : c0641f74
r10: c1ffc7a0  r9 : 6901b118  r8 : 00000001
r7 : c0639a34  r6 : 0000001b  r5 : a00000d3  r4 : c0645d70
r3 : c0645d78  r2 : 00000001  r1 : c0641ef0  r0 : c0645d70
Flags: nZCv  IRQs off  FIQs off  Mode SVC_32  ISA ARM  Segment none
Control: c020717f  Table: c020717f  DAC: 00000053
Process swapper (pid: 0, stack limit = 0xc0640188)
Stack: (0xc0641f60 to 0xc0642000)
1f60: 00384000 c08762e4 c0641f98 c0641f78 c063308c c021b144 00000000 00000000
1f80: 00000000 c0660b20 ffffffff c0641fa8 c0641f9c c06220ec c0633058 c0641fb8
1fa0: c0641fac c061f114 c06220dc c0641ff4 c0641fbc c061bb68 c061f0fc ffffffff
1fc0: ffffffff 00000000 c061b6cc c0639a34 c0660cd4 c0642038 c0639a30 c0645434
1fe0: c0204000 c06380f8 00000000 c0641ff8 c0208048 c061b954 00000000 00000000
Backtrace:
[<c021b138>] (clk_enable) from [<c063308c>] (pxa_timer_nodt_init+0x40/0x120)
 r5:c08762e4 r4:00384000
[<c063304c>] (pxa_timer_nodt_init) from [<c06220ec>] (sa1100_timer_init+0x1c/0x20)
 r6:ffffffff r5:c0660b20 r4:00000000
[<c06220d0>] (sa1100_timer_init) from [<c061f114>] (time_init+0x24/0x2c)
[<c061f0f0>] (time_init) from [<c061bb68>] (start_kernel+0x220/0x42c)
[<c061b948>] (start_kernel) from [<c0208048>] (0xc0208048)
 r10:c06380f8 r8:c0204000 r7:c0645434 r6:c0639a30 r5:c0642038 r4:c0660cd4
Code: bad PC value
---[ end trace 0000000000000000 ]---
Kernel panic - not syncing: Attempted to kill the idle task!

Fixes: ee3a4020 ("ARM: 8250/1: sa1100: provide OSTIMER0 clock for pxa_timer")
Acked-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>