soc: qcom: qmi_interface: Remove ineffective mutex lock from txn struct

The same QMI transaction data is synchronized using two mutex locks.

Remove ineffective transaction mutex lock because it is always
covered by QMI txn_lock with same purpose.

CRs-Fixed: 2470638
Change-Id: If53e006436c77d572b2d69507e1593e3d57e1cd4
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>