ecl: Magnetic declination use improvements
ecl: Magnetic declination use improvements

Fixes bugs causing learned or GEO lookup declination to not be used in some circumstances.

https://github.com/PX4/ecl/pull/518
https://github.com/PX4/ecl/pull/520

krbeverx/Firmware,dagar/Firmware,dagar/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,acfloria/Firmware,acfloria/Firmware,acfloria/Firmware,dagar/Firmware,PX4/Firmware,krbeverx/Firmware,Aerotenna/Firmware,Aerotenna/Firmware,dagar/Firmware,PX4/Firmware,krbeverx/Firmware,krbeverx/Firmware,Aerotenna/Firmware,krbeverx/Firmware,PX4/Firmware,mje-nz/PX4-Firmware,mje-nz/PX4-Firmware,PX4/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,acfloria/Firmware,Aerotenna/Firmware,Aerotenna/Firmware,mje-nz/PX4-Firmware,dagar/Firmware,PX4/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,PX4/Firmware,Aerotenna/Firmware,PX4/Firmware,dagar/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,Aerotenna/Firmware,dagar/Firmware