xfs: return bool from xfs_attr3_leaf_add

xfs_attr3_leaf_add only has two potential return values, indicating if the
entry could be added or not.  Replace the errno return with a bool so that
ENOSPC from it can't easily be confused with a real ENOSPC.

Remove the return value from the xfs_attr3_leaf_add_work helper entirely,
as it always return 0.

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