Input: alps - decode the position packet first

We should decode the position packet before the packet with the bitmap
data.  This way we can use the more accurate position info in
process_bitmap() to get better results.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>