ath11k: Use freq instead of channel number in rx path

As 6GHz cahnnel numbers overlap with those of 5GHz and 2GHz bands,
it is necessary to use frequency when determining the band info
in rx path.

Signed-off-by: Pradeep Kumar Chitrapu <pradeepc@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200603001724.12161-4-pradeepc@codeaurora.org