scftorture: Warn on individual scf_torture_init() error conditions

When running scftorture as a module, any scf_torture_init() issues will be
reflected in the error code from modprobe or insmod, as the case may be.
However, these error codes are not available when running scftorture
built-in, for example, when using the kvm.sh script.  This commit
therefore adds WARN_ON_ONCE() to allow distinguishing scf_torture_init()
errors when running scftorture built-in.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/scftorture.c

@@ -606,17 +606,17 @@ static int __init scf_torture_init(void)
 
 	if (onoff_interval > 0) {
 		firsterr = torture_onoff_init(onoff_holdoff * HZ, onoff_interval, NULL);
-		if (firsterr)
+		if (torture_init_error(firsterr))
 			goto unwind;
 	}
 	if (shutdown_secs > 0) {
 		firsterr = torture_shutdown_init(shutdown_secs, scf_torture_cleanup);
-		if (firsterr)
+		if (torture_init_error(firsterr))
 			goto unwind;
 	}
 	if (stutter > 0) {
 		firsterr = torture_stutter_init(stutter, stutter);
-		if (firsterr)
+		if (torture_init_error(firsterr))
 			goto unwind;
 	}
 
@@ -637,12 +637,12 @@ static int __init scf_torture_init(void)
 		scf_stats_p[i].cpu = i;
 		firsterr = torture_create_kthread(scftorture_invoker, (void *)&scf_stats_p[i],
 						  scf_stats_p[i].task);
-		if (firsterr)
+		if (torture_init_error(firsterr))
 			goto unwind;
 	}
 	if (stat_interval > 0) {
 		firsterr = torture_create_kthread(scf_torture_stats, NULL, scf_torture_stats_task);
-		if (firsterr)
+		if (torture_init_error(firsterr))
 			goto unwind;
 	}