drm/exynos: remove duplicated check for suspend

The same check is placed twice in fimd/decon_update_plane(), remove
one of them.

Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Reviewed-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>