soc: qcom: msm_smd: check for NULL pointer and return

Check for NULL pointer is present in WARN_ON() which prints message
and continue the execution.

Check and return the execution flow to avoid the NULL pointer
access.

CRs-Fixed: 2207243
Change-Id: I7d73762f3ead06afb97ddf762d9ea7f3fe466d26
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>