spi: s3c64xx: replace clock disabling with runtime PM suspend call in remove function

Simplify s3c64xx_spi_remove by replacing the clock disabling with calling
runtime PM suspend which does the same.
Waking up the device if it was suspended wouldn't be strictly needed
for this driver but using pm_runtime_get_sync is cleaner and makes
s3c64xx_spi_remove more consistent with the runtime PM handling in
s3c64xx_spi_setup.

pm_runtime_force_suspend does most of the work for us:
disabling the clocks, disabling runtime PM and setting it to
"suspended" state.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>