gyro_calibration: make sure to initialize sensor_correction properly
gyro_calibration: make sure to initialize sensor_correction properly

if it's not published yet or published with low frequency, this makes sure
we have valid data.

also:
- _sensor_correction -> sensor_correction
- remove unnecessary init of sensor_correction_sub

jlecoeur/Firmware,dagar/Firmware,PX4/Firmware,mcgill-robotics/Firmware,jlecoeur/Firmware,krbeverx/Firmware,jlecoeur/Firmware,dagar/Firmware,dagar/Firmware,Aerotenna/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,Aerotenna/Firmware,mje-nz/PX4-Firmware,jlecoeur/Firmware,PX4/Firmware,jlecoeur/Firmware,krbeverx/Firmware,dagar/Firmware,acfloria/Firmware,jlecoeur/Firmware,jlecoeur/Firmware,mcgill-robotics/Firmware,krbeverx/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,mje-nz/PX4-Firmware,PX4/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,acfloria/Firmware,Aerotenna/Firmware,mcgill-robotics/Firmware,dagar/Firmware,krbeverx/Firmware,acfloria/Firmware,mcgill-robotics/Firmware,PX4/Firmware,mcgill-robotics/Firmware,mje-nz/PX4-Firmware,dagar/Firmware,acfloria/Firmware,Aerotenna/Firmware,PX4/Firmware,PX4/Firmware,mcgill-robotics/Firmware,Aerotenna/Firmware,mcgill-robotics/Firmware,dagar/Firmware,acfloria/Firmware,Aerotenna/Firmware,Aerotenna/Firmware,krbeverx/Firmware,PX4/Firmware,jlecoeur/Firmware