drivers/gps: fix segfault when parsing arguments
drivers/gps: fix segfault when parsing arguments

running gps command without parameters results in segfault
due to illegal access to unallocated memory

Signed-off-by: Nicolae Rosia <207aa917b021b404c269e8647897b2cc6117052a@gmail.com>

jlecoeur/Firmware,jlecoeur/Firmware,PX4/Firmware,Aerotenna/Firmware,krbeverx/Firmware,mcgill-robotics/Firmware,mje-nz/PX4-Firmware,darknight-007/Firmware,PX4/Firmware,acfloria/Firmware,dagar/Firmware,acfloria/Firmware,PX4/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,Aerotenna/Firmware,Aerotenna/Firmware,jlecoeur/Firmware,darknight-007/Firmware,mcgill-robotics/Firmware,mcgill-robotics/Firmware,acfloria/Firmware,PX4/Firmware,dagar/Firmware,mje-nz/PX4-Firmware,PX4/Firmware,mje-nz/PX4-Firmware,mje-nz/PX4-Firmware,dagar/Firmware,acfloria/Firmware,jlecoeur/Firmware,jlecoeur/Firmware,acfloria/Firmware,mje-nz/PX4-Firmware,darknight-007/Firmware,krbeverx/Firmware,krbeverx/Firmware,mje-nz/PX4-Firmware,krbeverx/Firmware,jlecoeur/Firmware,jlecoeur/Firmware,jlecoeur/Firmware,Aerotenna/Firmware,Aerotenna/Firmware,Aerotenna/Firmware,acfloria/Firmware,krbeverx/Firmware,krbeverx/Firmware,mcgill-robotics/Firmware,Aerotenna/Firmware,dagar/Firmware,dagar/Firmware,dagar/Firmware,dagar/Firmware,mcgill-robotics/Firmware,mcgill-robotics/Firmware,darknight-007/Firmware,PX4/Firmware,mcgill-robotics/Firmware,darknight-007/Firmware,PX4/Firmware,acfloria/Firmware