ath11k: avoid burst time conversion logic

WMI_VDEV_SET_WMM_PARAMS commmand expects the txoplimit param in the units of
32 microseconds. convert the txop unit from 32 microseconds to absolute
microseconds leads to the higher burst values which is incorrect. so no need
to convert the txop unit from 32 microseconds to absolute microseconds.

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