soc: qcom: pil: Initialize variable to avoid invalid access

Initialize dp_fw to NULL so that we don't try to release it in the
error path err_invalid_fw.

CRs-Fixed: 1095243
Change-Id: I18f549102e626dc788e8fa56d6bb1ea28efe4f88
Signed-off-by: Puja Gupta <pujag@codeaurora.org>