parisc: irq: Make irq_stack_union static to avoid sparse warning

Signed-off-by: Helge Deller <deller@gmx.de>

Author: hdeller

arch/parisc/kernel/irq.c

@@ -365,7 +365,7 @@ union irq_stack_union {
 	volatile unsigned int lock[1];
 };
 
-DEFINE_PER_CPU(union irq_stack_union, irq_stack_union) = {
+static DEFINE_PER_CPU(union irq_stack_union, irq_stack_union) = {
 		.slock = { 1,1,1,1 },
 	};
 #endif