irqchip/armada-370-xp: Make syscore_ops static

The armada_370_xp_mpic_syscore_ops structure is not exported or
declared anywhere. Fix the following warning by making it static:

drivers/irqchip/irq-armada-370-xp.c:544:20: warning: symbol 'armada_370_xp_mpic_syscore_ops' was not declared. Should it be static?
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Link: https://lkml.kernel.org/r/1465408533-13906-1-git-send-email-ben.dooks@codethink.co.ukSigned-off-by: Jason Cooper <jason@lakedaemon.net>

drivers/irqchip/irq-armada-370-xp.c

@@ -541,7 +541,7 @@ static void armada_370_xp_mpic_resume(void)
 		writel(1, per_cpu_int_base + ARMADA_370_XP_INT_CLEAR_MASK_OFFS);
 }
 
-struct syscore_ops armada_370_xp_mpic_syscore_ops = {
+static struct syscore_ops armada_370_xp_mpic_syscore_ops = {
 	.suspend	= armada_370_xp_mpic_suspend,
 	.resume		= armada_370_xp_mpic_resume,
 };