genirq/irq_sim: Initialize work context pointers properly

Initialize `ops` member's pointers properly by using kzalloc() instead of
kmalloc() when allocating the simulation work context. Otherwise the
pointers contain random content leading to invalid dereferencing.

Signed-off-by: Gyeyoung Baek <gye976@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20250612124827.63259-1-gye976@gmail.com