drivers/block/drbd: 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: NJulia Lawall <julia@diku.dk>
Signed-off-by: NPhilipp Reisner <philipp.reisner@linbit.com>

drivers/block/drbd/drbd_receiver.c

@@ -3945,7 +3945,7 @@ static int drbd_do_auth(struct drbd_conf *mdev)
 	}
 
 	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;