TI DaVinci EMAC: Fix asymmetric handling of packets in NAPI Poll function.

The current implementation of NAPI poll function in the driver does not service
Rx packets, error condition even if a single Tx packet gets serviced in
the napi poll call. This behavior severely affects performance for specific use
cases. This patch modifies the poll function implementation to service tx/rx
packets in an identical manner.

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