fmu: fix PPM publication if RC_SERIAL_PORT is not defined
fmu: fix PPM publication if RC_SERIAL_PORT is not defined

Before, the RC channel was published as fast as the fmu was running
(around 200Hz in unarmed state).

And fix code style.

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