x86/mm: Fix cpumask_of_node() error condition

When CONFIG_DEBUG_PER_CPU_MAPS=y we validate that the @node argument of
cpumask_of_node() is a valid node_id. It however forgets to check for
negative numbers. Fix this by explicitly casting to unsigned int.

  (unsigned)node >= nr_node_ids

verifies: 0 <= node < nr_node_ids

Also ammend the error message to match the condition.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Yunsheng Lin <linyunsheng@huawei.com>
Link: https://lkml.kernel.org/r/20190903075352.GY2369@hirez.programming.kicks-ass.netSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/mm/numa.c

@@ -861,9 +861,9 @@ void numa_remove_cpu(int cpu)
  */
 const struct cpumask *cpumask_of_node(int node)
 {
-	if (node >= nr_node_ids) {
+	if ((unsigned)node >= nr_node_ids) {
 		printk(KERN_WARNING
-			"cpumask_of_node(%d): node > nr_node_ids(%u)\n",
+			"cpumask_of_node(%d): (unsigned)node >= nr_node_ids(%u)\n",
 			node, nr_node_ids);
 		dump_stack();
 		return cpu_none_mask;