Properly free drm plane during creation of sprites

If we fail to allocate space for a new drm_sprite, then we should
properly call drmModeFreePlane (not free) to release the drm plane.

Signed-off-by: Chris Michael <cp.michael@samsung.com>

src/compositor-drm.c

@@ -2107,7 +2107,7 @@ create_sprites(struct drm_compositor *ec)
 		if (!sprite) {
 			weston_log("%s: out of memory\n",
 				__func__);
-			free(plane);
+			drmModeFreePlane(plane);
 			continue;
 		}