hidraw: Make HIDIOCGRDESCSIZE ioctl return report descriptor size

defined by hardware rather than cached one to match HIDIOCGRDESC ioctl.
This fixes errors reported by hid-tools being run against /dev/hidraw#
device node belonging to driver which overloads report descriptor.

MFC after: 1 week

(cherry picked from commit f988d7fa050e4886cdeb9483a039e75d58c31883)