soc: qcom: qmi_interface: use qmi txn_lock to avoid use after free of txn

In some cases txn is freed before mutex_unlock() API returns and
causing invalid pointer access.

Protect the txn with qmi txn_lock to avoid the invalid pointer access.

CRs-Fixed: 2470638
Change-Id: I05ccde9a77d2913a396c8505bb3199b28fc021c2
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>