irqchip/ti-sci-inta: Fix unsigned comparison to zero

ti_sci_inta_xlate_irq() return -ENOENT on fail, p_hwirq
should be int type.

Fixes: 5c4b585d ("irqchip/ti-sci-inta: Add support for INTA directly connecting to GIC")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Acked-by: Lokesh Vutla <lokeshvutla@ti.com>
Link: https://lore.kernel.org/r/20200826035430.21060-1-yuehaibing@huawei.com