wifi: ath12k: Use initializers for QMI message buffers

Currently most of the QMI messaging functions use memset() to zero out
the QMI message buffers. Prefer to use a {} initializer to allow the
compiler to generate optimized code and avoid the function call
overhead.

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-v2-3-53343af953d5@quicinc.com