const: make block_device_operations const

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 5d23ffa..cc923a5 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -722,7 +722,7 @@
 	return error;
 }
 
-static struct block_device_operations nbd_fops =
+static const struct block_device_operations nbd_fops =
 {
 	.owner =	THIS_MODULE,
 	.locked_ioctl =	nbd_ioctl,