linux-imx

Input: mk712 - update documentation web link

At the mentioned address there's nothing found. By searching information
on the controller chip still can be found, so update the link to the
resulting page.

Signed-off-by: Martin Kepplinger <martink@posteo.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>