touch_input is stored in wacom_shared for pen data to report touch
switch status. It is possible, although we didn't see it happen on
Linux yet, that pen data is procesed before touch interface is
fully probed.

As a by-product of this patch, it fixes the FreeBSD issue reported
by Denis Akiyakov http://www.spinics.net/lists/linux-input/msg33971.htmlReviewed-by: NHans Petter Selasky <hps@selasky.org>
Tested-by: NDenis Akiyakov <d.akiyakov@gmail.com>
Signed-off-by: NPing Cheng <pingc@wacom.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>