drm/exynos: gsc: fix wrong pm_runtime state

At probe time, gsc clock is not enabled, so pm_runtime state should
be deactive. So this patch removes pm_runtime_set_active() from
gsc_probe().

Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Signed-off-by: Inki Dae <inki.dae@samsung.com>