liquidio: remove unnecessary variable assignment

gcc points out an useless assignment that was added during code refactoring:

drivers/net/ethernet/cavium/liquidio/lio_ethtool.c: In function 'octnet_intrmod_callback':
drivers/net/ethernet/cavium/liquidio/lio_ethtool.c:1315:59: error: parameter 'oct_dev' set but not used [-Werror=unused-but-set-parameter]

This is harmless but can clearly be remove to avoid the warning.

Fixes: 50c0add5

 ("liquidio: refactor interrupt moderation code")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>