HID: ignore digitizer usage Undefined (0x00)

SMART Technologies has recommended this change to fix a problem reported
with SMART Board series interactive whiteboards.

A description of the device-specific symptom follows:

  When the board is connected my mouse bounces up to the top left corner.

Bjorn has tested this fix with model SB680.

Tested-by: Bjorn Behrendt <bbehrendt@msjvermont.org>
Signed-off-by: Forest Bond <forest@alittletooquiet.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>