EKF: Fix critical bug in fusion of yaw and declination observations
EKF: Fix critical bug in fusion of yaw and declination observations

This bug was in the derivation and resulted from use of a tan instead of an atan operator. The derivations have been reworked and the updated auto-code has been imported as part of this patch.

PX4/ecl,PX4/ecl,PX4/ecl,PX4/ecl,PX4/ecl