Plane: fixed yaw on fwd transition in tilt quadplanes

this fixes the coordinated turn calculation for yaw rate in tilt
quadplanes, and also only applies it if demanding at least 10 degrees
roll.

this fixes an issue when the pilot has a small roll demand in FBWA
from slightly off roll RC trim

thanks to Henry for helping diagnose this!

ArduPlane/quadplane.cpp

@@ -899,11 +899,11 @@ void QuadPlane::update_yaw_target(void)
      */
     float aspeed;
     bool have_airspeed = ahrs.airspeed_estimate(aspeed);
-    if (have_airspeed) {
+    if (have_airspeed && labs(plane.nav_roll_cd)>1000) {
         float dt = (now - tilt.transition_yaw_set_ms) * 0.001;
         // calculate the yaw rate to achieve the desired turn rate
         const float airspeed_min = MAX(plane.aparm.airspeed_min,5);
-        const float yaw_rate_cds = degrees(GRAVITY_MSS/MAX(aspeed,airspeed_min) * sinf(radians(plane.nav_roll_cd*0.01)))*100;
+        const float yaw_rate_cds = fixedwing_turn_rate(plane.nav_roll_cd*0.01, MAX(aspeed,airspeed_min))*100;
         tilt.transition_yaw_cd += yaw_rate_cds * dt;
     }
     tilt.transition_yaw_set_ms = now;