drm/mediatek: Use drm_mode_get_hv_timing() to populate plane clip rectangle

Use drm_mode_get_hv_timing() to fill out the plane clip rectangle.

No functional changes as the code already uses crtc_state->mode
to populate the clip, which is also what drm_mode_get_hv_timing()
uses.

Once everyone agrees on this we can move the clip handling into
drm_atomic_helper_check_plane_state().

Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: CK Hu <ck.hu@mediatek.com>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171123190502.28449-8-ville.syrjala@linux.intel.comAcked-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/mediatek/mtk_drm_plane.c

@@ -108,8 +108,9 @@ static int mtk_plane_atomic_check(struct drm_plane *plane,
 	if (IS_ERR(crtc_state))
 		return PTR_ERR(crtc_state);
 
-	clip.x2 = crtc_state->mode.hdisplay;
-	clip.y2 = crtc_state->mode.vdisplay;
+	if (crtc_state->enable)
+		drm_mode_get_hv_timing(&crtc_state->mode,
+				       &clip.x2, &clip.y2);
 
 	return drm_atomic_helper_check_plane_state(state, crtc_state, &clip,
 						   DRM_PLANE_HELPER_NO_SCALING,