powerpc: Fix incorrect comment about interrupt stack allocation

We now allow interrupt stacks anywhere in the first segment which can be
256M or 1TB. Fix the comment.
Signed-off-by: NAnton Blanchard <anton@samba.org>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/setup_64.c

@@ -437,8 +437,8 @@ static void __init irqstack_early_init(void)
 	unsigned int i;
 
 	/*
-	 * interrupt stacks must be under 256MB, we cannot afford to take
-	 * SLB misses on them.
+	 * Interrupt stacks must be in the first segment since we
+	 * cannot afford to take SLB misses on them.
 	 */
 	for_each_possible_cpu(i) {
 		softirq_ctx[i] = (struct thread_info *)