net/macb: fix sparse warning

this patch fixes following sparse warning:

macb.c:2038:26: warning: symbol 'gem_ethtool_ops' was not declared. Should it be static?

Alongside drops exporting of gem_ethtool_ops as there is no need.

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>