Servo test: Ensure we only close an open FD

src/systemcmds/tests/test_servo.c

@@ -116,6 +116,8 @@ int test_servo(int argc, char *argv[])
 	printf("Advancing channel 1 to 1800\n");
 	result = ioctl(fd, PWM_SERVO_SET(1), 1800);
 out:
-	close(fd);
+	if (fd >= 0) {
+		close(fd);
+	}
 	return 0;
 }