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>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1464179407-9004-1-git-send-email-tjakobi@math.uni-bielefeld.de