sh_eth: Change handling of IRQ

Handling of IRQ of the SH7763/SH7764 CPU which sh_eth supported was
changed.
This revises it for this change.

Signed-off-by: Nobuhiro Iwamatsu <iwamatsu.nobuhiro@renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>