const missing in usbdrv.h and usbdrv.c

[physnoct]

Several messages like these appeared during compilation:
error: variable ‘usbDescriptorStringVendor’ must be const in order to be put into read-only section by means of ‘attribute((progmem))’
PROGMEM int usbDescriptorStringVendor[] = {

By adding 'const' to the definitions in usbdrv.h and usbdrv.c, the compilation completes normally, as shown below:
PROGMEM const int usbDescriptorStringVendor[] = {