ethernet: atarilance: mark init function static

The init function is only referenced locally, so it should be static to
avoid this warning:

drivers/net/ethernet/amd/atarilance.c:370:28: error: no previous prototype for 'atarilance_probe' [-Werror=missing-prototypes]

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Yang Yingliang <yangyingliang@huawei.com>
Link: https://lore.kernel.org/r/20230810122528.1220434-2-arnd@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>