xfs: Lift -ENOSPC handler from xfs_attr_leaf_addname

Lift -ENOSPC handler from xfs_attr_leaf_addname.  This will help to
reorganize transitions between the attr forms later.

Signed-off-by: Allison Collins <allison.henderson@oracle.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Acked-by: Dave Chinner <dchinner@redhat.com>