drivers:drm:exynos_drm_gsc:Fix wrong assignment in gsc_bind()

cocci reported a double assignment problem. Upon reviewing previous
commits, it appears this may actually be an incorrect assignment.

Fixes: 8b955034 ("drm/ipp: clean up debug messages")
Signed-off-by: Yuesong Li <liyuesong@vivo.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>