[PATCH] hrtimer: Add a missing bracket and hide `migration_base' on !SMP

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

Commit
   68b2c8c1e4210 ("hrtimer: Don't take expiry_lock when timer is currently migrated")

missed to add a bracket at the end of the if statement leading to
compile errors.
Since that commit the variable `migration_base' is always used but only
available on SMP configuration thus leading to another compile error.
The changelog says
  "The timer base and base->cpu_base cannot be NULL in the code path"

so it is safe to limit this check to SMP configurations only.

Add the missing bracket to the if statement and hide `migration_base'
behind CONFIG_SMP bars.

Fixes: 68b2c8c1e4210 ("hrtimer: Don't take expiry_lock when timer is currently migrated")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/time/hrtimer.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index f5a1a5e16216c..bc84c74ae5b96 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1216,12 +1216,16 @@ void hrtimer_cancel_wait_running(const struct hrtimer *timer)
 {
 	/* Lockless read. Prevent the compiler from reloading it below */
 	struct hrtimer_clock_base *base = READ_ONCE(timer->base);
+	bool is_migration_base = false;
 
 	/*
 	 * Just relax if the timer expires in hard interrupt context or if
 	 * it is currently on the migration base.
 	 */
-	if (!timer->is_soft || base == &migration_base)
+#ifdef CONFIG_SMP
+	is_migration_base = base == &migration_base;
+#endif
+	if (timer->is_soft || is_migration_base) {
 		cpu_relax();
 		return;
 	}
-- 
2.23.0