8139cp: Fix one possible deadloop in cp_rx_poll

When cp_rx_poll does not get enough packet, it will check the rx
interrupt status again. If so, it will jumpt to rx_status_loop again.
But the goto jump resets the rx variable as zero too.

As a result, it causes one possible deadloop. Assume this case,
rx_status_loop only gets the packet count which is less than budget,
and (cpr16(IntrStatus) & cp_rx_intr_mask) condition is always true.
It causes the deadloop happens and system is blocked.

Signed-off-by: Gao Feng <fgao@ikuai8.com>
Signed-off-by: David S. Miller <davem@davemloft.net>