clocksource/drivers/nxp-pit: Fix IRQ leak on cpuhp_setup_state error path

In the Linux kernel, the following vulnerability has been resolved:

clocksource/drivers/nxp-pit: Fix IRQ leak on cpuhp_setup_state error path

When cpuhp_setup_state fails after pit_clockevent_per_cpu_init has
successfully called request_irq, the error handling jumps directly to
out_pit_clocksource_unregister without freeing the registered IRQ.

This leaks the IRQ line and, since kfree(pit) follows, leaves a
dangling pointer registered as the interrupt handler's dev_id,
potentially leading to a use-after-free if the IRQ fires afterwards.

Fix it by calling pit_clockevent_per_cpu_exit to properly release the
IRQ before falling through to the existing cleanup chain.