s390/qeth: don't warn for napi with 0 budget

Calling napi->poll() with 0 budget is a legitimate use by netpoll.

Fixes: a1c3ed4c ("qeth: NAPI support for l2 and l3 discipline")
Signed-off-by: NJulian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/s390/net/qeth_core_main.c

@@ -5447,7 +5447,6 @@ static int qeth_extract_skbs(struct qeth_card *card, int budget,
 {
 	int work_done = 0;
 
-	WARN_ON_ONCE(!budget);
 	*done = false;
 
 	while (budget) {