~/Downloads/r5u870 $ make
make -C /lib/modules/3.13.0-24-generic/build M=/home/xxx/Downloads/r5u870 V=0 modules
make[1]: Entering directory `/usr/src/linux-headers-3.13.0-24-generic'
  CC [M]  /home/xxx/Downloads/r5u870/usbcam/usbcam_dev.o
/home/xxx/Downloads/r5u870/usbcam/usbcam_dev.c: In function ‘usbcam_register_mod’:
/home/xxx/Downloads/r5u870/usbcam/usbcam_dev.c:502:3: error: implicit declaration of function ‘err’ [-Werror=implicit-function-declaration]
   err("%s: Failed to allocate usbcam_minidrv_t", __FUNCTION__);
   ^
cc1: some warnings being treated as errors
make[3]: *** [/home/xxx/Downloads/r5u870/usbcam/usbcam_dev.o] Error 1
make[2]: *** [/home/xxx/Downloads/r5u870/usbcam] Error 2
make[1]: *** [_module_/home/xxx/Downloads/r5u870] Error 2
make[1]: Leaving directory `/usr/src/linux-headers-3.13.0-24-generic'
make: *** [all] Error 2