drivers: net: cpsw: remove tx event processing in rx napi poll

With commit c03abd84 ("net: ethernet: cpsw: don't requests IRQs
we don't use") common isr and napi are separated into separate tx isr
and rx isr/napi, but still in rx napi tx events are handled. So removing
the tx event handling in rx napi.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>