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>

fs/ext4/inode.c

@@ -5263,7 +5263,7 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
 			error = PTR_ERR(handle);
 			goto err_out;
 		}
-		error = vfs_dq_transfer(inode, attr) ? -EDQUOT : 0;
+		error = dquot_transfer(inode, attr);
 		if (error) {
 			ext4_journal_stop(handle);
 			return error;