sh_eth: Fix memleak in sh_mdio_release

Allocated memory for IRQs should be freed when releasing the mii_bus

Signed-off-by: Denis Kirjanov <dkirjanov@kernel.org>
Acked-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Signed-off-by: David S. Miller <davem@davemloft.net>