dquot: cleanup dquot transfer routine

Get rid of the transfer dquot operation - it is now always called from
the filesystem and if a filesystem really needs it's own (which none
currently does) it can just call into it's own routine directly.

Rename the now static low-level dquot_transfer helper to __dquot_transfer
and vfs_dq_transfer to dquot_transfer to have a consistent namespace,
and make the new dquot_transfer return a normal negative errno value
which all callers expect.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/ufs/truncate.c b/fs/ufs/truncate.c
index 56ab31f..87bbab6 100644
--- a/fs/ufs/truncate.c
+++ b/fs/ufs/truncate.c
@@ -520,7 +520,7 @@
 
 	if ((ia_valid & ATTR_UID && attr->ia_uid != inode->i_uid) ||
 	    (ia_valid & ATTR_GID && attr->ia_gid != inode->i_gid)) {
-		error = vfs_dq_transfer(inode, attr) ? -EDQUOT : 0;
+		error = dquot_transfer(inode, attr);
 		if (error)
 			return error;
 	}