wifi: ath12k: Remove unnecessary struct qmi_txn initializers

Currently most of the ath12k QMI messaging functions define their
struct qmi_txn variables with a {} initializer. However, all of these
functions subsequently call qmi_txn_init(), and the very first thing
that function does is zero the struct. Hence, the initializers are
unnecessary. Since these consume code space and cpu cycles, remove
them.

No functional changes, compile tested only.

Signed-off-by: Jeff Johnson <quic_jjohnson@quicinc.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://msgid.link/20240111-qmi-cleanup-v2-1-53343af953d5@quicinc.com