xfs: drop the scrub file's iolock when transaction allocation fails

If the transaction allocation in the !orphanage_available case of
xrep_nlinks_repair_inode fails, we need to drop the IOLOCK of the file
being scrubbed before exiting.

Found by fuzzing u3.sfdir3.list[1].name = zeroes in xfs/1546.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>