AP_OSD: use AUX_PWM_TRIGGER_LOW and AUX_PWM_TRIGGER_HIGH

libraries/AP_OSD/AP_OSD_ParamScreen.cpp

@@ -406,9 +406,9 @@ RC_Channel::AuxSwitchPos AP_OSD_ParamScreen::get_channel_pos(uint8_t rcmapchan)
     // switch is reversed if 'reversed' option set on channel and switches reverse is allowed by RC_OPTIONS
     bool switch_reversed = chan->get_reverse() && rc().switch_reverse_allowed();
 
-    if (in < 1300) {
+    if (in < RC_Channel::AUX_PWM_TRIGGER_LOW) {
         return switch_reversed ? RC_Channel::AuxSwitchPos::HIGH : RC_Channel::AuxSwitchPos::LOW;
-    } else if (in > 1700) {
+    } else if (in > RC_Channel::AUX_PWM_TRIGGER_HIGH) {
         return switch_reversed ? RC_Channel::AuxSwitchPos::LOW : RC_Channel::AuxSwitchPos::HIGH;
     } else {
         return RC_Channel::AuxSwitchPos::MIDDLE;