net/macb: remove macb_get_drvinfo()

This function has little meaning so remove it altogether and
let ethtool core fill in the fields automatically.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Reviewed-by: Ben Hutchings <bhutchings@solarflare.com>
Tested-by: Joachim Eastwood <manabian@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>