intel: Fix memory leak in event of mip tree allocation failure

Signed-off-by: Brian Paul <brianp@vmware.com>

src/mesa/drivers/dri/intel/intel_mipmap_tree.c

@@ -134,8 +134,10 @@ intel_miptree_create(struct intel_context *intel,
    /*
     * pitch == 0 || height == 0  indicates the null texture
     */
-   if (!mt || !mt->pitch || !mt->total_height)
+   if (!mt || !mt->pitch || !mt->total_height) {
+      free(mt);
       return NULL;
+   }
 
    mt->region = intel_region_alloc(intel,
 				   tiling,