LoongArch: KVM: Replace eiointc_enable_irq() with eiointc_update_irq()

Function eiointc_enable_irq() checks mask value with char type, and
call eiointc_update_irq() eventually. Function eiointc_update_irq()
will update one single irq status directly.

Here it can check mask value with unsigned long type and call function
eiointc_update_irq(), that is simple and direct.

Signed-off-by: Bibo Mao <maobibo@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>