direct_IO: remove rw from a_ops->direct_IO()

Now that no one is using rw, remove it completely.

Signed-off-by: Omar Sandoval <osandov@osandov.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/ext4/inode.c

@@ -3089,8 +3089,8 @@ retake_lock:
 	return ret;
 }
 
-static ssize_t ext4_direct_IO(int rw, struct kiocb *iocb,
-			      struct iov_iter *iter, loff_t offset)
+static ssize_t ext4_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
+			      loff_t offset)
 {
 	struct file *file = iocb->ki_filp;
 	struct inode *inode = file->f_mapping->host;