drivers: gpio: rpi_pico: route ISR to the right irq_ctrl

gpio_rpi_isr() always addressed io_bank0->proc0_irq_ctrl, so any
interrupts taken while code was running on core 1 were invisible and
left pending.
Use get_core_num() to pick proc1_irq_ctrl when the ISR executes on core
1, ensuring callbacks fire from both cores.
Also fix stray `iobank0_hw` symbol for the correct `io_bank0_hw`.

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>