mavlink streams: add return in all cases

Generally not needed here, but GCC produced an error when compiling with
-finstrument-functions.

src/modules/mavlink/streams/ACTUATOR_CONTROL_TARGET.hpp

@@ -57,6 +57,8 @@ public:
 		case 3:
 			return "ACTUATOR_CONTROL_TARGET3";
 		}
+
+		return "ACTUATOR_CONTROL_TARGET";
 	}
 
 	static constexpr uint16_t get_id_static() { return MAVLINK_MSG_ID_ACTUATOR_CONTROL_TARGET; }

src/modules/mavlink/streams/SERVO_OUTPUT_RAW.hpp

@@ -51,6 +51,8 @@ public:
 		case 1:
 			return "SERVO_OUTPUT_RAW_1";
 		}
+
+		return "SERVO_OUTPUT_RAW";
 	}
 
 	static constexpr uint16_t get_id_static() { return MAVLINK_MSG_ID_SERVO_OUTPUT_RAW; }