irqchip/loongson-liointc: Fix build error for LoongArch

liointc driver is shared by MIPS and LoongArch, this patch adjust the
code to fix build error for LoongArch.

Acked-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: WANG Xuerui <git@xen0n.name>
Reviewed-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>