videoscale: fix memory leak

In gst_video_scale_fixate_caps () it can goto done without freeing the memory
of the tmp GstStructure. This makes it go out of scope and leak.

CID #1265766

gst/videoscale/gstvideoscale.c

@@ -980,6 +980,7 @@ gst_video_scale_fixate_caps (GstBaseTransform * base, GstPadDirection direction,
               &to_par_n, &to_par_d)) {
         GST_ELEMENT_ERROR (base, CORE, NEGOTIATION, (NULL),
             ("Error calculating the output scaled size - integer overflow"));
+        gst_structure_free (tmp);
         goto done;
       }