irqchip/ti-sci-inta: Fix return value about devm_ioremap_resource()

When call function devm_ioremap_resource(), we should use IS_ERR()
to check the return value and return PTR_ERR() if failed.

Fixes: 9f1463b8 ("irqchip/ti-sci-inta: Add support for Interrupt Aggregator driver")
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com>
Link: https://lore.kernel.org/r/1591437017-5295-2-git-send-email-yangtiezhu@loongson.cn