Trackpoint buttons detection fails on ThinkPad 570 and 470 series,
this makes the middle button of the trackpoint to not being recogized.
As I don't believe there is any trackpoint with less than 3 buttons this
patch just assumes three buttons when the extended button information
read fails.
Signed-off-by: NOscar Campos <oscar.campos@member.fsf.org>
Acked-by: NPeter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>