block: make xenbus device id constant

Author: Márton Németh <nm127@freemail.hu>

The ids field of the struct xenbus_device_id is constant in 
so it is worth to make blkfront_ids also constant.

The semantic match that finds this kind of pattern is as follows:
(http://coccinelle.lip6.fr/)

// 
@r@
disable decl_init,const_decl_init;
identifier I1, I2, x;
@@
	struct I1 {
	  ...
	  const struct I2 *x;
	  ...
	};
@s@
identifier r.I1, y;
identifier r.x, E;
@@
	struct I1 y = {
	  .x = E,
	};
@c@
identifier r.I2;
identifier s.E;
@@
	const struct I2 E[] = ... ;
@depends on !c@
identifier r.I2;
identifier s.E;
@@
+	const
	struct I2 E[] = ...;
// 

Signed-off-by: Márton Németh 
Cc: Julia Lawall 
Cc: cocci@diku.dk
Signed-off-by: Jens Axboe 

---
 drivers/block/xen-blkfront.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
 
diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
index 05a31e5..a84702d 100644
--- a/drivers/block/xen-blkfront.c
+++ b/drivers/block/xen-blkfront.c
@@ -1050,7 +1050,7 @@ static const struct block_device_operations xlvbd_block_fops =
 };
 
 
-static struct xenbus_device_id blkfront_ids[] = {
+static const struct xenbus_device_id blkfront_ids[] = {
 	{ "vbd" },
 	{ "" }
 };