spi: pxa2xx: toggle clocks on suspend if not disabled by runtime PM

If PM_RUNTIME is enabled, it is easy to trigger the following backtrace
on pxa2xx hosts:

------------[ cut here ]------------
WARNING: CPU: 0 PID: 1 at /home/lumag/linux/arch/arm/mach-pxa/clock.c:35 clk_disable+0xa0/0xa8()
Modules linked in:
CPU: 0 PID: 1 Comm: swapper Not tainted 3.17.0-00007-g1b3d2ee-dirty #104
[<c000de68>] (unwind_backtrace) from [<c000c078>] (show_stack+0x10/0x14)
[<c000c078>] (show_stack) from [<c001d75c>] (warn_slowpath_common+0x6c/0x8c)
[<c001d75c>] (warn_slowpath_common) from [<c001d818>] (warn_slowpath_null+0x1c/0x24)
[<c001d818>] (warn_slowpath_null) from [<c0015e80>] (clk_disable+0xa0/0xa8)
[<c0015e80>] (clk_disable) from [<c02507f8>] (pxa2xx_spi_suspend+0x2c/0x34)
[<c02507f8>] (pxa2xx_spi_suspend) from [<c0200360>] (platform_pm_suspend+0x2c/0x54)
[<c0200360>] (platform_pm_suspend) from [<c0207fec>] (dpm_run_callback.isra.14+0x2c/0x74)
[<c0207fec>] (dpm_run_callback.isra.14) from [<c0209254>] (__device_suspend+0x120/0x2f8)
[<c0209254>] (__device_suspend) from [<c0209a94>] (dpm_suspend+0x50/0x208)
[<c0209a94>] (dpm_suspend) from [<c00455ac>] (suspend_devices_and_enter+0x8c/0x3a0)
[<c00455ac>] (suspend_devices_and_enter) from [<c0045ad4>] (pm_suspend+0x214/0x2a8)
[<c0045ad4>] (pm_suspend) from [<c04b5c34>] (test_suspend+0x14c/0x1dc)
[<c04b5c34>] (test_suspend) from [<c000880c>] (do_one_initcall+0x8c/0x1fc)
[<c000880c>] (do_one_initcall) from [<c04aecfc>] (kernel_init_freeable+0xf4/0x1b4)
[<c04aecfc>] (kernel_init_freeable) from [<c0378078>] (kernel_init+0x8/0xec)
[<c0378078>] (kernel_init) from [<c0009590>] (ret_from_fork+0x14/0x24)
---[ end trace 46524156d8faa4f6 ]---

This happens because suspend function tries to disable a clock that is
already disabled by runtime_suspend callback. Add if
(!pm_runtime_suspended()) checks to suspend/resume path.

Fixes: 7d94a505 (spi/pxa2xx: add support for runtime PM)
Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Reported-by: Andrea Adami <andrea.adami@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org