xfs: fix a memory leak

kmemleak reported that we don't free the parent pointer names here if we
found corruption.

Fixes: 0d29a20f ("xfs: scrub parent pointers")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>