xfs: Fix a comment on xfs_ail_delete

It doesn't return anything.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: Chandan Babu R <chandanbabu@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>