ehea: Remove force_irq logic in napi poll routine

commit 18604c54 (ehea: NAPI multi queue TX/RX path for SMP) added
driver specific logic for exiting napi mode. I'm not sure what it was
trying to solve and it should be up to the network stack to decide when
we are done polling so remove it.

v3:
[cascardo] Fixed extra parentheses.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>