Input: st1232 - fix reporting multitouch coordinates

For Sitronix st1633 multi-touch controller driver the coordinates reported
for multiple fingers were wrong, as it was always taking LSB of coordinates
from the first contact data.

Signed-off-by: Dixit Parmar <dixitparmar19@gmail.com>
Reviewed-by: Martin Kepplinger <martink@posteo.de>
Cc: stable@vger.kernel.org
Fixes: 351e0592

 ("Input: st1232 - add support for st1633")
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=204561
Link: https://lore.kernel.org/r/1566209314-21767-1-git-send-email-dixitparmar19@gmail.com
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>