irqchip/mmp: Make icu_irq_chip variable static const

File-scope 'icu_irq_chip' is not used outside of this unit and is not
modified anywhere, so make it static const to silence sparse warning:

irq-mmp.c:139:17: warning: symbol 'icu_irq_chip' was not declared. Should it be static?

Signed-off-by: Krzysztof Kozlowski <[e-mail]>
Signed-off-by: Thomas Gleixner <[e-mail]>
Link: https://patch.msgid.link/[e-mail]

drivers/irqchip/irq-mmp.c

···
 	}
 }
 
-struct irq_chip icu_irq_chip = {
+static const struct irq_chip icu_irq_chip = {
 	.name		= "icu_irq",
 	.irq_mask	= icu_mask_irq,
 	.irq_mask_ack	= icu_mask_ack_irq,