When the left touchpad button gets pressed, and then the trackpoint is
moved, and then the button is released, the following happens:

1) touchpad packet is received, touchpad evdev node reports BTN_LEFT 1

2) pointing stick packet is received, the hw will report a BTN_LEFT 1 in
   this packet because when the trackstick is active it communicates the
   combined touchpad + pointing stick buttons in the trackstick packet,
   since alps_report_bare_ps2_packet passes NULL (*) for the dev2 parameter
   to alps_report_buttons the combining is not detected and the
   pointing stick evdev node will also report BTN_LEFT 1

3) on release of the button a pointing stick packet with BTN_LEFT 0 is
   received and the pointing stick evdev node will report BTN_LEFT 0

Note how because of the passing as NULL for dev2 the touchpad evdev node
will never send BTN_LEFT 0 in this scenario leading to a stuck mouse button.

This is a regression in 4.0 introduced by commit 04aae283
("Input: ALPS - do not mix trackstick and external PS/2 mouse data")

This commit fixes this by passing in the touchpad evdev as dev2 parameter
when calling alps_report_buttons for the pointingstick on alps v2 devices,
so that alps_report_buttons correctly detect that we're already reporting
the button as pressed via the touchpad evdev node, and will also send the
release event there.

Cc: stable@vger.kernel.org # 4.0
Reported-by: Hans de Bruin <jmdebruin@xmsnet.nl>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Pali Rohár <pali.rohar@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>