block: don't call into the driver for BLKFLSBUF

BLKFLSBUF is entirely contained in the block core, and there is no
good reason to give the driver a hook into processing it.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NJens Axboe <axboe@kernel.dk>

block/ioctl.c

@@ -369,15 +369,8 @@ static inline int is_unrecognized_ioctl(int ret)
 static int blkdev_flushbuf(struct block_device *bdev, fmode_t mode,
 		unsigned cmd, unsigned long arg)
 {
-	int ret;
-
 	if (!capable(CAP_SYS_ADMIN))
 		return -EACCES;
-
-	ret = __blkdev_driver_ioctl(bdev, mode, cmd, arg);
-	if (!is_unrecognized_ioctl(ret))
-		return ret;
-
 	fsync_bdev(bdev);
 	invalidate_bdev(bdev);
 	return 0;