qtnfmac: update channel switch command to support 6GHz band

With an addition of 6GHz band support, channel number can no longer be
used to uniquely identify a specific channel. Modify channel switch
command to use chandef data.

Signed-off-by: Igor Mitsyanko <igor.mitsyanko.os@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>