HID: wacom: Fail probe if HID_GENERIC device has unknown device_type

The last patch was careful to maintain backwards-compatible behavior
by forcing device_type to BTN_TOOL_PEN (and printing a warning) if it
were still uninitialized after scanning the HID descriptor and applying
quirks. We should be more strict with HID_GENERIC devices, however,
since there is no a priori guarantee that it is a tablet or touchpad.
If the device_type is still uninitialized for a HID_GENERIC device then
we assume that it isn't something the driver can work with and so fail
the probe.

Signed-off-by: Jason Gerecke <jason.gerecke@wacom.com>
Reviewed-by: Ping Cheng <pingc@wacom.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>