Input: trackpoint - assume 3 buttons when buttons detection fails

commit 293b915f upstream.

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: Oscar Campos <oscar.campos@member.fsf.org>
Acked-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Aaron Ma <aaron.ma@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/input/mouse/trackpoint.c

@@ -377,8 +377,8 @@ int trackpoint_detect(struct psmouse *psmouse, bool set_properties)
 		return 0;
 
 	if (trackpoint_read(&psmouse->ps2dev, TP_EXT_BTN, &button_info)) {
-		psmouse_warn(psmouse, "failed to get extended button data\n");
-		button_info = 0;
+		psmouse_warn(psmouse, "failed to get extended button data, assuming 3 buttons\n");
+		button_info = 0x33;
 	}
 
 	psmouse->private = kzalloc(sizeof(struct trackpoint_data), GFP_KERNEL);