xfs: Replace macro XFS_DQ_TO_QIP with a function

In preparation for combined pquota/gquota support, for the sake
of readability, change the macro to an inline function.

Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>

fs/xfs/xfs_dquot.c

@@ -573,7 +573,7 @@ xfs_qm_dqtobp(
 	xfs_bmbt_irec_t map;
 	int		nmaps = 1, error;
 	xfs_buf_t	*bp;
-	xfs_inode_t	*quotip = XFS_DQ_TO_QIP(dqp);
+	struct xfs_inode	*quotip = xfs_dq_to_quota_inode(dqp);
 	xfs_mount_t	*mp = dqp->q_mount;
 	xfs_dqid_t	id = be32_to_cpu(dqp->q_core.d_id);
 	xfs_trans_t	*tp = (tpp ? *tpp : NULL);