motor_ramp remove unreachable code (#7973)

src/systemcmds/motor_ramp/motor_ramp.cpp

@@ -211,9 +211,6 @@ int motor_ramp_main(int argc, char *argv[])
 					      motor_ramp_thread_main,
 					      (argv) ? (char *const *)&argv[2] : (char *const *)nullptr);
 	return 0;
-
-	usage("unrecognized command");
-	return 1;
 }
 
 bool min_pwm_valid(unsigned pwm_value)