xfs: remove the incorrect comment about the b_pag field

The rbtree root is long gone.

Signed-off-by: Christoph Hellwig <[email protected]>
Reviewed-by: Darrick J. Wong <[email protected]>
Acked-by: Dave Chinner <[email protected]>
Signed-off-by: Carlos Maiolino <[email protected]>

Author: Christoph Hellwig

fs/xfs/xfs_buf.h

@@ -187,7 +187,7 @@ struct xfs_buf {
 	int			b_io_error;	/* internal IO error state */
 	wait_queue_head_t	b_waiters;	/* unpin waiters */
 	struct list_head	b_list;
-	struct xfs_perag	*b_pag;		/* contains rbtree root */
+	struct xfs_perag	*b_pag;
 	struct xfs_mount	*b_mount;
 	struct xfs_buftarg	*b_target;	/* buffer target (device) */
 	void			*b_addr;	/* virtual address of buffer */