drm: Add local 'plane' variable for tmp->primary

Clean up the ugly tmp->primary-> stuff in
__drm_mode_set_config_internal() with a local plane variable.

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180405151400.11326-13-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_crtc.c

@@ -469,8 +469,11 @@ static int __drm_mode_set_config_internal(struct drm_mode_set *set,
 	 * connectors from it), hence we need to refcount the fbs across all
 	 * crtcs. Atomic modeset will have saner semantics ...
 	 */
-	drm_for_each_crtc(tmp, crtc->dev)
-		tmp->primary->old_fb = tmp->primary->fb;
+	drm_for_each_crtc(tmp, crtc->dev) {
+		struct drm_plane *plane = tmp->primary;
+
+		plane->old_fb = plane->fb;
+	}
 
 	fb = set->fb;
 
@@ -481,11 +484,13 @@ static int __drm_mode_set_config_internal(struct drm_mode_set *set,
 	}
 
 	drm_for_each_crtc(tmp, crtc->dev) {
-		if (tmp->primary->fb)
-			drm_framebuffer_get(tmp->primary->fb);
-		if (tmp->primary->old_fb)
-			drm_framebuffer_put(tmp->primary->old_fb);
-		tmp->primary->old_fb = NULL;
+		struct drm_plane *plane = tmp->primary;
+
+		if (plane->fb)
+			drm_framebuffer_get(plane->fb);
+		if (plane->old_fb)
+			drm_framebuffer_put(plane->old_fb);
+		plane->old_fb = NULL;
 	}
 
 	return ret;