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>
diff --git a/fs/block_dev.c b/fs/block_dev.c
index bc23afd..6e3de63 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -146,8 +146,7 @@
 }
 
 static ssize_t
-blkdev_direct_IO(int rw, struct kiocb *iocb, struct iov_iter *iter,
-			loff_t offset)
+blkdev_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;