gpio: loongson-64bit: Fix a less than zero check on an unsigned int struct field

gpio: loongson-64bit: Fix a less than zero check on an unsigned int struct field

Currently the error check from the call to platform_get_irq is always
false because an unsigned int chip->irq.parents[i] is being used to
to perform the less than zero error check. Fix this by using the int
variable ret to perform the check.

Fixes: 03c146cb6cd1 ("gpio: loongson-64bit: Add support for Loongson-2K0300 SoC")
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Reviewed-by: Yao Zi <ziyao@disroot.org>
Link: https://lore.kernel.org/r/20250909190356.870000-1-colin.i.king@gmail.com
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>