xfs: use discontiguous xfs_buf support in dabuf wrappers

[Dan Carpenter]

Hello Dave Chinner,

This is a semi-automatic email about new static checker warnings.

The patch 3605431fb973: "xfs: use discontiguous xfs_buf support in
dabuf wrappers" from Jun 22, 2012, leads to the following Smatch
complaint:

fs/xfs/xfs_da_btree.c:2113 xfs_da_get_buf()
	 error: we previously assumed 'bp' could be null (see line 2111)

fs/xfs/xfs_da_btree.c
  2110					    mapp, nmap, 0);
  2111		error = bp ? bp->b_error : XFS_ERROR(EIO);
  2112		if (error) {
  2113			xfs_trans_brelse(trans, bp);
                        ^^^^^^^^^^^^^^^^^^^^^^^^^^
If bp is NULL here then it causes an Oops.

  2114			goto out_free;
  2115		}

regards,
dan carpenter