irqchip/irq-mvebu-icu: Make legacy_bindings static

Fix the following sparse warning:

drivers/irqchip/irq-mvebu-icu.c:69:1: warning: symbol 'legacy_bindings'
was not declared. Should it be static?

Reported-by: Hulk Robot <[e-mail]>
Signed-off-by: Jason Yan <[e-mail]>
Signed-off-by: Marc Zyngier <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/irqchip/irq-mvebu-icu.c

···
 	unsigned int type;
 };
 
-DEFINE_STATIC_KEY_FALSE(legacy_bindings);
+static DEFINE_STATIC_KEY_FALSE(legacy_bindings);
 
 static void mvebu_icu_init(struct mvebu_icu *icu,
 			   struct mvebu_icu_msi_data *msi_data,