pwm: add missing exit

src/systemcmds/pwm/pwm.c

@@ -649,7 +649,7 @@ pwm_main(int argc, char *argv[])
 				ret = ioctl(fd, PWM_SERVO_SET_FORCE_FAILSAFE, 0);
 			}
 		}
-
+		exit(0);
 	}
 
 	usage("specify arm|disarm|rate|failsafe|disarmed|min|max|test|info");