net: asix: change the type of asix_set_sw/hw_mii to static

The functions of asix_set_sw/hw_mii are not called in other files, so
change them to static.

Signed-off-by: Zhengchao Shao <shaozhengchao@huawei.com>
Link: https://lore.kernel.org/r/20220704123448.128980-1-shaozhengchao@huawei.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>