rcutorture: Check for rcu_torture_fqs creation errors

The return value from torture_create_kthread() is currently ignored
when creating the rcu_torture_fqs kthread.  This commit therefore
captures the return value so that it can be tested for errors.
Signed-off-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: NJosh Triplett <josh@joshtriplett.org>

kernel/rcu/rcutorture.c

@@ -1577,7 +1577,8 @@ rcu_torture_init(void)
 		fqs_duration = 0;
 	if (fqs_duration) {
 		/* Create the fqs thread */
-		torture_create_kthread(rcu_torture_fqs, NULL, fqs_task);
+		firsterr = torture_create_kthread(rcu_torture_fqs, NULL,
+						  fqs_task);
 		if (firsterr)
 			goto unwind;
 	}