Input: alps - fix v4 button press recognition

Since the change to struct input_mt_pos some variables are now bitfields
instead of integers. Automatic conversion from integer to bitfield entry
destroys information, therefore enforce boolean interpretation instead.

Link: https://bugzilla.redhat.com/show_bug.cgi?id=1114768
Fixes: 02d04254a5df ("Input: alps - use struct input_mt_pos to track coordinates")
Signed-off-by: Andreas Bosch <linux@progandy.de>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>