r8169: simplify counter handling

The counter handling functions can only fail if rtl8169_do_counters()
times out. In the poll function we emit an error message in case of
timeout, therefore we don't have to propagate the timeout all the
way up just to print another message basically saying the same.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>