xfs: add helper for verifying checksums on xfs_bufs

Many/most callers of xfs_verify_cksum() pass bp->b_addr and
BBTOB(bp->b_length) as the first 2 args.  Add a helper
which can just accept the bp and the crc offset, and work
it out on its own, for brevity.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_alloc.c

@@ -485,8 +485,7 @@ xfs_agfl_read_verify(
 	if (!xfs_sb_version_hascrc(&mp->m_sb))
 		return;
 
-	agfl_ok = xfs_verify_cksum(bp->b_addr, BBTOB(bp->b_length),
-				   XFS_AGFL_CRC_OFF);
+	agfl_ok = xfs_buf_verify_cksum(bp, XFS_AGFL_CRC_OFF);
 
 	agfl_ok = agfl_ok && xfs_agfl_verify(bp);
 
@@ -2240,8 +2239,7 @@ xfs_agf_read_verify(
 	int		agf_ok = 1;
 
 	if (xfs_sb_version_hascrc(&mp->m_sb))
-		agf_ok = xfs_verify_cksum(bp->b_addr, BBTOB(bp->b_length),
-					  XFS_AGF_CRC_OFF);
+		agf_ok = xfs_buf_verify_cksum(bp, XFS_AGF_CRC_OFF);
 
 	agf_ok = agf_ok && xfs_agf_verify(mp, bp);