ath11k: avoid WMM param truncation

In conf_tx() mac operation callback, we are truncating the tx
params cw_min and cw_max due to lower data type cast. so modified
the data type of cwmin and cwmax to avoid the trucation issue.

Signed-off-by: Karthikeyan Periyasamy <periyasa@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>