drm/rcar-du: 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>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180123170857.13818-1-ville.syrjala@linux.intel.com
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

drivers/gpu/drm/rcar-du/rcar_du_plane.c

@@ -572,7 +572,7 @@ int __rcar_du_plane_atomic_check(struct drm_plane *plane,
 {
 	struct drm_device *dev = plane->dev;
 	struct drm_crtc_state *crtc_state;
-	struct drm_rect clip;
+	struct drm_rect clip = {};
 	int ret;
 
 	if (!state->crtc) {
@@ -589,10 +589,9 @@ int __rcar_du_plane_atomic_check(struct drm_plane *plane,
 	if (IS_ERR(crtc_state))
 		return PTR_ERR(crtc_state);
 
-	clip.x1 = 0;
-	clip.y1 = 0;
-	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);
 
 	ret = drm_atomic_helper_check_plane_state(state, crtc_state, &clip,
 						  DRM_PLANE_HELPER_NO_SCALING,