spi: s3c64xx: simplify suspend / resume handlers

The runtime PM suspend / resume handlers take care of the enabling/
disabling the clocks already. Therefore replace the duplicated
clock handling with pm_runtime_force_suspend/resume.

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