sparc64: fix sparse warning in traps_64.c

Fix following warning:
traps_64.c:2384:6: error: symbol 'die_if_kernel' redeclared with different type (originally declared at include/asm/bug.h:23) - different modifiers

Add proper __noreturn to the implementation to fix this
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

arch/sparc/kernel/traps_64.c

@@ -2381,7 +2381,7 @@ static inline struct reg_window *kernel_stack_up(struct reg_window *rw)
 	return (struct reg_window *) (fp + STACK_BIAS);
 }
 
-void die_if_kernel(char *str, struct pt_regs *regs)
+void __noreturn die_if_kernel(char *str, struct pt_regs *regs)
 {
 	static int die_counter;
 	int count = 0;