wcn36xx: Silence error about unsupported smd event 188

Sometimes the firmware sends a HAL_DEL_BA_IND, the prima driver silently
ignore this message so let's do the same to silence the error message.

Cc: Nicolas Dechesne <nicolas.dechesne@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>