HID: wacom: correct misreported EKR ring values

The EKR ring claims a range of 0 to 71 but actually reports
values 1 to 72. The ring is used in relative mode so this
change should not affect users.

Signed-off-by: Aaron Armstrong Skomra <aaron.skomra@wacom.com>
Fixes: 72b236d6

 ("HID: wacom: Add support for Express Key Remote.")
Cc: <stable@vger.kernel.org> # v4.3+
Reviewed-by: Ping Cheng <ping.cheng@wacom.com>
Reviewed-by: Jason Gerecke <jason.gerecke@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>