irqchip/exiu: Fix the index of fwspec for IRQ type

Since fwspec->param_count of ACPI node is two, the index of IRQ type
in fwspec->param[] should be 1 rather than 2.

Fixes: 3d090a36 ("irqchip/exiu: Implement ACPI support")
Signed-off-by: Chen Baozi <chenbaozi@phytium.com.cn>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Link: https://lore.kernel.org/r/20201117032015.11805-1-cbz@baozis.org
Cc: stable@vger.kernel.org