xfs: fix broken bhold behavior in xrep_roll_ag_trans

In xrep_roll_ag_trans, the transaction roll will always set sc->tp to
the new transaction, even if committing the old one fails.  A bare
transaction roll leaves the buffer(s) locked but not joined to the new
transaction, so it's not necessary to release the hold if the roll
fails.  Remove the incorrect xfs_trans_bhold_release calls.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>