l3gd20: add argc check and use px4_getopt
l3gd20: add argc check and use px4_getopt

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