msm: platsmp-8625: modify pen_release variable to volatile

Since pen_release is a shared variable between cpus. By marking it
as volatile, compiler won't cache that variable into registers and
won't optimize the code which access pen_release variable.

Change-Id: Ib5b7aa5932b35d64d05f9e4a4672df2bb9207c59
Signed-off-by: tirupathireddy <tirupath@codeaurora.org>