HID: wacom: Enable pad device for older Bamboo Touch tablets

Commit 862cf553 ("HID: wacom: Introduce a new WACOM_DEVICETYPE_PAD device_type")
neglected to set the WACOM_DEVICETYPE_PAD flag for older two-finger Bamboo
Touch tablets. Not only does this result in the pad device not appearing when
such a tablet is plugged in, but also causes a segfault when 'wacom_bpt_touch'
tries to send pad events. This patch adds the flag to resolve these issues.

Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>