dcache: restore error on restart in prepend_path

We need to restore all variables including error (as it is done in the
upstream kernel). The variable error was errorneously not restored when
backporting the patch ede4cebc
(prepend_path() needs to reinitialize dentry/vfsmount/mnt on restarts).

This should be applied only to the 3.12 series.
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>

fs/dcache.c

@@ -2893,6 +2893,7 @@ static int prepend_path(const struct path *path,
 restart:
 	bptr = *buffer;
 	blen = *buflen;
+	error = 0;
 	dentry = path->dentry;
 	vfsmnt = path->mnt;
 	mnt = real_mount(vfsmnt);