xfs: adjust xfs_bmap_add_attrfork for metadir

Online repair might use the xfs_bmap_add_attrfork to repair a file in
the metadata directory tree if (say) the metadata file lacks the correct
parent pointers.  In that case, it is not correct to check that the file
is dqattached -- metadata files must be not have /any/ dquot attached at
all.  Adjust the assertions appropriately.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>