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_da_btree.c

@@ -214,8 +214,7 @@ xfs_da3_node_read_verify(
 
 	switch (be16_to_cpu(info->magic)) {
 		case XFS_DA3_NODE_MAGIC:
-			if (!xfs_verify_cksum(bp->b_addr, BBTOB(bp->b_length),
-					      XFS_DA3_NODE_CRC_OFF))
+			if (!xfs_buf_verify_cksum(bp, XFS_DA3_NODE_CRC_OFF))
 				break;
 			/* fall through */
 		case XFS_DA_NODE_MAGIC: