workqueue: fix build problem on !CONFIG_SMP

Commit f3421797 (workqueue: implement unbound workqueue) incorrectly
tested CONFIG_SMP as part of a C expression in alloc/free_cwqs().  As
CONFIG_SMP is not defined in UP, this breaks build.  Fix it by using

Found during linux-next build test.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>

kernel/workqueue.c

@@ -2615,11 +2615,15 @@ static int alloc_cwqs(struct workqueue_struct *wq)
 	const size_t size = sizeof(struct cpu_workqueue_struct);
 	const size_t align = max_t(size_t, 1 << WORK_STRUCT_FLAG_BITS,
 				   __alignof__(unsigned long long));
+#ifdef CONFIG_SMP
+	bool percpu = !(wq->flags & WQ_UNBOUND);
+#else
+	bool percpu = false;
+#endif
 
-	if (CONFIG_SMP && !(wq->flags & WQ_UNBOUND)) {
-		/* on SMP, percpu allocator can align itself */
+	if (percpu)
 		wq->cpu_wq.pcpu = __alloc_percpu(size, align);
-	} else {
+	else {
 		void *ptr;
 
 		/*
@@ -2641,7 +2645,13 @@ static int alloc_cwqs(struct workqueue_struct *wq)
 
 static void free_cwqs(struct workqueue_struct *wq)
 {
-	if (CONFIG_SMP && !(wq->flags & WQ_UNBOUND))
+#ifdef CONFIG_SMP
+	bool percpu = !(wq->flags & WQ_UNBOUND);
+#else
+	bool percpu = false;
+#endif
+
+	if (percpu)
 		free_percpu(wq->cpu_wq.pcpu);
 	else if (wq->cpu_wq.single) {
 		/* the pointer to free is stored right after the cwq */