net: lpc_eth: Driver cleanup

This patch removes some nowadays superfluous definitions (one unused define and
an obsolete function forward declaration) and corrects a netdev_err() to
netdev_dbg().

Signed-off-by: Roland Stigge <stigge@antcom.de>
Signed-off-by: Alexandre Pereira da Silva <aletes.xgr@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>