wcn36xx: Use HW_VALUE_CHANNEL macro to get channel number

Uses HW_VALUE_CHANNEL() to extract the channel number from a
struct ieee80211_channel->hw_value. Once done we can use the upper bits of
the hw_value to encode PHY related data.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200910150708.2179043-3-bryan.odonoghue@linaro.org