[led] propagate error from set_led() to the caller

Do not lose error condition by always returning 0 from set_led.
None of the calls to set_led checks for return value at the moment so
none of API consumers in base is affected.

PR:		231567
Submitted by:	Bertrand Petit <bsdpr@phoe.frmug.org>
MFC after:	1 week

sys/dev/led/led.c

@@ -261,7 +261,7 @@ led_set(char const *name, char const *cmd)
 	mtx_unlock(&led_mtx);
 	if (sb != NULL)
 		sbuf_delete(sb);
-	return (0);
+	return (error);
 }
 
 static struct cdevsw led_cdevsw = {