tests/xics: Ensure no compiler optimisations in delay()

In case it would be tempted to "read ahead" the delay function

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

tests/xics/xics.c

@@ -12,8 +12,8 @@ void delay(void)
 {
 	static volatile int i;
 
-	for (i = 0; i < 10; ++i)
+	for (i = 0; i < 16; ++i)
-		;
+		__asm__ volatile("" : : : "memory");
 }
 
 void print_number(unsigned int i) // only for i = 0-999