HID: Make report_descriptor available for all devices

Currently the sysfs report_descriptor attribute is only available if the device
is claimed.  We have the descriptor before we even create the device node, so
just instantiate report_descriptor statically.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>