sh_eth: remove #ifdef around sh_eth_select_mii()

We can simply remove #ifdef'fery around sh_eth_select_mii(). We have to annotate
it with '__maybe_unused' then.

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
[Sergei: added the changelog, reworded the subject, changing the prefix.]
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>