soc: qcom: Initialize message pointer with NULL

During service locator call there is a chance in which
resp message is used or freed while uninitialized.So to
prevent it initialize the same with NULL.

Change-Id: I65f854e184606684ce2ca711f19cf61d26c1ecb5
Signed-off-by: Gaurav Kohli <gkohli@codeaurora.org>