gpio: ljca: Fix duplicated IRQ mapping

gpio: ljca: Fix duplicated IRQ mapping

The generic_handle_domain_irq() function resolves the hardware IRQ
internally. The driver performed a duplicative mapping by calling
irq_find_mapping() first, which could lead to an RCU stall.

Delete the redundant irq_find_mapping() call and pass the hardware IRQ
directly to generic_handle_domain_irq().

Fixes: c5a4b6fd31e8 ("gpio: Add support for Intel LJCA USB GPIO driver")
Signed-off-by: Haotian Zhang <vulab@iscas.ac.cn>
Link: https://lore.kernel.org/r/20251023070231.1305-1-vulab@iscas.ac.cn
[Bartosz: remove unused variable]
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>