Plane: fixed use of expo values in radio

backport of https://github.com/ArduPilot/ardupilot/pull/19751

ArduPlane/radio.cpp

@@ -410,10 +410,10 @@ float Plane::roll_in_expo(bool use_dz) const
 
 float Plane::pitch_in_expo(bool use_dz) const
 {
-    return channel_expo(channel_pitch, g2.man_expo_roll, use_dz);
+    return channel_expo(channel_pitch, g2.man_expo_pitch, use_dz);
 }
 
 float Plane::rudder_in_expo(bool use_dz) const
 {
-    return channel_expo(channel_rudder, g2.man_expo_roll, use_dz);
+    return channel_expo(channel_rudder, g2.man_expo_rudder, use_dz);
 }