i am having the same error. GobiSerial make does not work.
khadas@Khadas:/media/khadas/disk/for_Linux/Sierra_Driver/GobiSerial$ sudo make
[sudo] password for khadas:
rm -rf *.o *~ core .depend .*.cmd *.ko *.mod.c .tmp_versions Module.* modules.order .cache.mk *.o.ur-safe
make -C /lib/modules/4.9.224/build M=/media/khadas/disk/for_Linux/Sierra_Driver/GobiSerial modules
make[1]: Entering directory '/usr/src/linux-headers-4.9.224'
CC [M] /media/khadas/disk/for_Linux/Sierra_Driver/GobiSerial/GobiSerial.o
/media/khadas/disk/for_Linux/Sierra_Driver/GobiSerial/GobiSerial.c:242:2: error: #warning "Assuming disc_mutex is locked external to the module" [-Werror=cpp]
#warning "Assuming disc_mutex is locked external to the module"
^~~~~~~
cc1: all warnings being treated as errors
scripts/Makefile.build:340: recipe for target '/media/khadas/disk/for_Linux/Sierra_Driver/GobiSerial/GobiSerial.o' failed
make[2]: *** [/media/khadas/disk/for_Linux/Sierra_Driver/GobiSerial/GobiSerial.o] Error 1
Makefile:1653: recipe for target '_module_/media/khadas/disk/for_Linux/Sierra_Driver/GobiSerial' failed
make[1]: *** [_module_/media/khadas/disk/for_Linux/Sierra_Driver/GobiSerial] Error 2
make[1]: Leaving directory '/usr/src/linux-headers-4.9.224'
Makefile:25: recipe for target 'all' failed
make: *** [all] Error 2