AP_Motors: add override keyword to get_motor_mask

libraries/AP_Motors/AP_MotorsCoax.h

@@ -47,7 +47,7 @@ public:
 
     // get_motor_mask - returns a bitmask of which outputs are being used for motors or servos (1 means being used)
     //  this can be used to ensure other pwm outputs (i.e. for servos) do not conflict
-    virtual uint16_t    get_motor_mask();
+    uint16_t            get_motor_mask() override;
 
 protected:
     // output - sends commands to the motors

libraries/AP_Motors/AP_MotorsMatrix.h

@@ -46,7 +46,7 @@ public:
 
     // get_motor_mask - returns a bitmask of which outputs are being used for motors (1 means being used)
     //  this can be used to ensure other pwm outputs (i.e. for servos) do not conflict
-    uint16_t            get_motor_mask();
+    uint16_t            get_motor_mask() override;
 
 protected:
     // output - sends commands to the motors

libraries/AP_Motors/AP_MotorsSingle.h

@@ -47,7 +47,7 @@ public:
 
     // get_motor_mask - returns a bitmask of which outputs are being used for motors or servos (1 means being used)
     //  this can be used to ensure other pwm outputs (i.e. for servos) do not conflict
-    virtual uint16_t    get_motor_mask();
+    uint16_t            get_motor_mask() override;
 
 protected:
     // output - sends commands to the motors

libraries/AP_Motors/AP_MotorsTailsitter.h

@@ -27,7 +27,7 @@ public:
     void output_to_motors();
 
     // return 0 motor mask
-    uint16_t get_motor_mask() { return 0; }
+    uint16_t get_motor_mask() override { return 0; }
 
 protected:
     // calculate motor outputs

libraries/AP_Motors/AP_MotorsTri.h

@@ -42,7 +42,7 @@ public:
 
     // get_motor_mask - returns a bitmask of which outputs are being used for motors or servos (1 means being used)
     //  this can be used to ensure other pwm outputs (i.e. for servos) do not conflict
-    virtual uint16_t    get_motor_mask();
+    uint16_t            get_motor_mask() override;
 
     // output a thrust to all motors that match a given motor
     // mask. This is used to control tiltrotor motors in forward