fs: simplify the blockdev_direct_IO prototype

Simple filesystems always pass inode->i_sb_bdev as the block device
argument, and never need a end_io handler.  Let's simply things for
them and for my grepping activity by dropping these arguments.  The
only thing not falling into that scheme is ext4, which passes and
end_io handler without needing special flags (yet), but given how
messy the direct I/O code there is use of __blockdev_direct_IO
in one instead of two out of three cases isn't going to make a large
difference anyway.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
index 06e7c76..a8a58f6 100644
--- a/fs/ext2/inode.c
+++ b/fs/ext2/inode.c
@@ -843,8 +843,8 @@
 	struct inode *inode = mapping->host;
 	ssize_t ret;
 
-	ret = blockdev_direct_IO(rw, iocb, inode, inode->i_sb->s_bdev,
-				iov, offset, nr_segs, ext2_get_block, NULL);
+	ret = blockdev_direct_IO(rw, iocb, inode, iov, offset, nr_segs,
+				 ext2_get_block);
 	if (ret < 0 && (rw & WRITE))
 		ext2_write_failed(mapping, offset + iov_length(iov, nr_segs));
 	return ret;