enic: enic_ethtool: fix sparse warning

this patch fixes following sparse warning:

enic_ethtool.c:95:6: warning: symbol 'enic_intr_coal_set_rx' was not declared. Should it be static?

Signed-off-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>