irqchip/aspeed-scu-ic: Fix irq_of_parse_and_map() return value

The irq_of_parse_and_map() returns 0 on failure, not a negative ERRNO.

Fixes: 04f60590 ("irqchip: Add Aspeed SCU interrupt controller")
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220423094227.33148-2-krzysztof.kozlowski@linaro.org