[media] exynos-gsc: Fixup clock management at ->remove()

[media] exynos-gsc: Fixup clock management at ->remove()

To make sure the clock is fully gated in ->remove(), we first need to
to bring the device into full power by invoking pm_runtime_get_sync().

Then, let's both unprepare and disable the clock.

[mszyprow: rebased onto v4.9-rc4]

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Javier Martinez Canillas <javier@osg.samsung.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>