smsc911x: Fix Console Hang when bringing the interface down.

In the NAPI poll function, check for netif_running() is unnecassary.
In addition to associated runtime overhead, it also results in
continuous softirq loop when the interface is brought down under heavy
traffic(tested with Traffic Generator).Once the interface is disabled,
the poll function always returns zero(with the check for netif_running)
and napi_complete() would never get called resulting in softirq loop.

Signed-off-by: Sriramakrishnan <srk@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>