quota: Split dquot_quota_sync() to writeback and cache flushing part

Split off part of dquot_quota_sync() which writes dquots into a quota file
to a separate function. In the next patch we will use the function from
filesystems and we do not want to abuse ->quota_sync quotactl callback more
than necessary.

Acked-by: Steven Whitehouse <swhiteho@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/gfs2/quota.h b/fs/gfs2/quota.h
index 90bf1c3..f25d98b 100644
--- a/fs/gfs2/quota.h
+++ b/fs/gfs2/quota.h
@@ -26,7 +26,7 @@
 extern void gfs2_quota_change(struct gfs2_inode *ip, s64 change,
 			      u32 uid, u32 gid);
 
-extern int gfs2_quota_sync(struct super_block *sb, int type, int wait);
+extern int gfs2_quota_sync(struct super_block *sb, int type);
 extern int gfs2_quota_refresh(struct gfs2_sbd *sdp, int user, u32 id);
 
 extern int gfs2_quota_init(struct gfs2_sbd *sdp);