xfs: simplify xfs_attr_remove_args

Directly return from the subfunctions and avoid the error variable.  Also
remove the not really needed dp local variable.

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