HID: wacom: fix problems when device is not a valid USB device

The wacom driver accepts devices of more than just USB types, but some
code paths can cause problems if the device being controlled is not a
USB device due to a lack of checking.  Add the needed checks to ensure
that the USB device accesses are only happening on a "real" USB device,
and not one on some other bus.

Cc: Jiri Kosina <jikos@kernel.org>
Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: linux-input@vger.kernel.org
Cc: stable@vger.kernel.org
Tested-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Link: https://lore.kernel.org/r/20211201183503.2373082-2-gregkh@linuxfoundation.org