virtio_blk: remove multichar constant.

drivers/block/virtio_blk.c:228:13: warning: multi-character character constant
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>
Cc: john cooper <john.cooper@redhat.com>

drivers/block/virtio_blk.c

@@ -225,7 +225,7 @@ static int virtblk_ioctl(struct block_device *bdev, fmode_t mode,
 	struct gendisk *disk = bdev->bd_disk;
 	struct virtio_blk *vblk = disk->private_data;
 
-	if (cmd == 'VBID') {
+	if (cmd == 0x56424944) { /* 'VBID' */
 		void __user *usr_data = (void __user *)data;
 		char id_str[VIRTIO_BLK_ID_BYTES];
 		int err;