drm/exynos: use logical AND in exynos_drm_plane_check_size()

The current bitwise AND should result in the same assembler
but this is what the code is actually supposed to do.

Signed-off-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Signed-off-by: Inki Dae <inki.dae@samsung.com>