ashtech gps: fix compiler warning in configure
ashtech gps: fix compiler warning in configure

the warning is:
error: ignoring return value of ‘ssize_t write(int, const void*, size_t)’, declared with attribute warn_unused_result [-Werror=unused-result]

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