xfs: don't return an error from xfs_update_last_rtgroup_size for !XFS_RT

Non-rtg file systems have a fake RT group even if they do not have a RT
device, and thus an rgcount of 1.  Ensure xfs_update_last_rtgroup_size
doesn't fail when called for !XFS_RT to handle this case.

Fixes: 87fe4c3 ("xfs: create incore realtime group structures")
Reported-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>

Author: Christoph Hellwig

fs/xfs/libxfs/xfs_rtgroup.h

@@ -272,7 +272,7 @@ static inline int xfs_initialize_rtgroups(struct xfs_mount *mp,
 }
 
 # define xfs_rtgroup_extents(mp, rgno)		(0)
-# define xfs_update_last_rtgroup_size(mp, rgno)	(-EOPNOTSUPP)
+# define xfs_update_last_rtgroup_size(mp, rgno)	(0)
 # define xfs_rtgroup_lock(rtg, gf)		((void)0)
 # define xfs_rtgroup_unlock(rtg, gf)		((void)0)
 # define xfs_rtgroup_trans_join(tp, rtg, gf)	((void)0)