input: touchscreen: Fix uninitialized variable usage in Atmel driver

Initialize variables that are passed by reference, so that
they can be used safely afterwards, irrespective of the
called function actions.

Change-Id: Ib52c1cbc621913b21eb9520d305327ff5fd154fe
Signed-off-by: Venkata Prahlad Valluru <vvalluru@codeaurora.org>