HID: roccat: allow readout of koneplus sensor register data

tcu sysfs attr was used to only control calibration process so far. Direct
sensor register access possibility has been revealed. Allowing readout of tcu
permits usage of this feature.

Signed-off-by: Stefan Achatz <erazor_de@users.sourceforge.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>