xfs: fix duplicate verification from xfs_qm_dqflush()

The pre-flush dquot verification in xfs_qm_dqflush() duplicates the
read verifier by checking the dquot in the on-disk buffer. Instead,
verify the in-core variant before it is flushed to the buffer.

Fixes: 7224fa48 ("xfs: add full xfs_dqblk verifier")
Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Allison Collins <allison.henderson@oracle.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>