natsemi: Avoid IntrStatus lossage if RX state machine resets.

This patch fixes the poll routine for the natsemi driver so that if the
driver detects an RX state machine lockup then no interrupts will be
lost while the driver recovers from that.

Signed-Off-By: Mark Brown <broonie@sirena.org.uk>
Signed-off-by: Jeff Garzik <jeff@garzik.org>