virStoragePoolDefParseSource: Don't leak @port

In a1c453dc08, during VIR_AUTOFREE() rewrite this wasn't done
properly. @port might be leaked because it's allocated in a for()
loop.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

src/conf/storage_conf.c

@@ -588,6 +588,7 @@ virStoragePoolDefParseSource(xmlXPathContextPtr ctxt,
                     goto cleanup;
                 }
             }
+            VIR_FREE(port);
         }
     }