GFS2: Hook gfs2_quota_sync into VFS via gfs2_quotactl_ops

The plan is to add further operations to the gfs2_quotactl_ops
in future patches. The sync operation is easy, so we start with
that one.

We plan to use the XFS quota control functions because they more
closely match the GFS2 ones.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
diff --git a/fs/gfs2/quota.h b/fs/gfs2/quota.h
index 437afa7..025d15b 100644
--- a/fs/gfs2/quota.h
+++ b/fs/gfs2/quota.h
@@ -50,5 +50,6 @@
 }
 
 extern int gfs2_shrink_qd_memory(int nr, gfp_t gfp_mask);
+extern const struct quotactl_ops gfs2_quotactl_ops;
 
 #endif /* __QUOTA_DOT_H__ */