linux_pwm_out: use PWM_MAIN parameter prefix

- this keeps things simpler for now across the old and new output
configuration

src/drivers/linux_pwm_out/linux_pwm_out.hpp

@@ -85,7 +85,7 @@ private:
 
 	void		update_params();
 
-	MixingOutput _mixing_output{"PWM", MAX_ACTUATORS, *this, MixingOutput::SchedulingPolicy::Auto, false};
+	MixingOutput _mixing_output{"PWM_MAIN", MAX_ACTUATORS, *this, MixingOutput::SchedulingPolicy::Auto, false};
 
 	uORB::SubscriptionInterval _parameter_update_sub{ORB_ID(parameter_update), 1_s};
 

src/drivers/linux_pwm_out/module.yaml

@@ -1,7 +1,7 @@
 module_name: PWM Output
 actuator_output:
   output_groups:
-    - param_prefix: PWM
+    - param_prefix: PWM_MAIN
       channel_label: 'Channel'
       standard_params:
         disarmed: { min: 800, max: 2200, default: 900 }