genirq/generic_chip: Constify irq_generic_chip_ops

The only usage of irq_generic_chip_ops is to pass its address to
irq_domain_add_linear() which takes a pointer to const struct
irq_domain_ops. Make it const to allow the compiler to put it in
read-only memory.

[ tglx: Fixed subject prefix ]
Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20211130214043.1257585-1-rikard.falkeborn@gmail.com

include/linux/irqdomain.h

@@ -131,7 +131,7 @@ struct irq_domain_ops {
 #endif
 };
 
-extern struct irq_domain_ops irq_generic_chip_ops;
+extern const struct irq_domain_ops irq_generic_chip_ops;
 
 struct irq_domain_chip_generic;
 

kernel/irq/generic-chip.c

@@ -451,7 +451,7 @@ static void irq_unmap_generic_chip(struct irq_domain *d, unsigned int virq)
 
 }
 
-struct irq_domain_ops irq_generic_chip_ops = {
+const struct irq_domain_ops irq_generic_chip_ops = {
 	.map	= irq_map_generic_chip,
 	.unmap  = irq_unmap_generic_chip,
 	.xlate	= irq_domain_xlate_onetwocell,