The memory leak was detected by kmemleak when running xfstests
overlay/051,053

Fixes: caf70cb2 ("ovl: cleanup orphan index entries")
Cc: <stable@vger.kernel.org> # v4.13
Signed-off-by: NAmir Goldstein <amir73il@gmail.com>
Signed-off-by: NMiklos Szeredi <mszeredi@redhat.com>