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_btree.c

@@ -243,8 +243,8 @@ xfs_btree_lblock_verify_crc(
 	struct xfs_buf		*bp)
 {
 	if (xfs_sb_version_hascrc(&bp->b_target->bt_mount->m_sb))
-		return xfs_verify_cksum(bp->b_addr, BBTOB(bp->b_length),
-					XFS_BTREE_LBLOCK_CRC_OFF);
+		return xfs_buf_verify_cksum(bp, XFS_BTREE_LBLOCK_CRC_OFF);
+
 	return true;
 }
 
@@ -276,8 +276,8 @@ xfs_btree_sblock_verify_crc(
 	struct xfs_buf		*bp)
 {
 	if (xfs_sb_version_hascrc(&bp->b_target->bt_mount->m_sb))
-		return xfs_verify_cksum(bp->b_addr, BBTOB(bp->b_length),
-					XFS_BTREE_SBLOCK_CRC_OFF);
+		return xfs_buf_verify_cksum(bp, XFS_BTREE_SBLOCK_CRC_OFF);
+
 	return true;
 }