msm: ipa: fix a static analysis issue at IPA unit-tests

Fix a static analysis issue at IPA driver,
IPA unit-tests I/S. Do not dereference a pointer even
if it can potentially be NULL.

CRs-Fixed: 1055710
Change-Id: Ie7eff49f136fe429ef10c6067ce7d8aae2694d3a
Signed-off-by: Ghanim Fodi <gfodi@codeaurora.org>