drivers/block/drbd/drbd_receiver.c: correct NULL test

Test the just-allocated value for NULL rather than some other value.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
expression x,y;
statement S;
@@

x = \(kmalloc\|kcalloc\|kzalloc\)(...);
(
if ((x) == NULL) S
|
if (
- y
+ x
== NULL)
S
)
// </smpl>

Signed-off-by: Julia Lawall <[e-mail]>
Cc: Lars Ellenberg <[e-mail]>
Cc: Philipp Reisner <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Jens Axboe <[e-mail]>

drivers/block/drbd/drbd_receiver.c

···
 	}
 
 	right_response = kmalloc(resp_size, GFP_NOIO);
-	if (response == NULL) {
+	if (right_response == NULL) {
 		dev_err(DEV, "kmalloc of right_response failed\n");
 		rv = 0;
 		goto fail;