Fix error exit path in __gnttab_map_grant_ref() to

put_domain() and hence avoid zombie domains.

Signed-off-by: Kouya Shimura <kouya@jp.fujitsu.com>

xen/common/grant_table.c

@@ -316,6 +316,7 @@ __gnttab_map_grant_ref(
     spin_unlock(&rd->grant_table->lock);
     (void)__put_user(rc, &uop->status);
     put_maptrack_handle(ld->grant_table, handle);
+    put_domain(rd);
     return rc;
 }