drbd: fix test of unsigned in _drbd_fault_random()

rsp->count is unsigned so the test does not work.
Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Cc: Lars Ellenberg <drbd-dev@lists.linbit.com>
Cc: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

drivers/block/drbd/drbd_main.c

@@ -3623,7 +3623,7 @@ _drbd_fault_random(struct fault_random_state *rsp)
 {
 	long refresh;
 
-	if (--rsp->count < 0) {
+	if (!rsp->count--) {
 		get_random_bytes(&refresh, sizeof(refresh));
 		rsp->state += refresh;
 		rsp->count = FAULT_RANDOM_REFRESH;