mac80211: s1g: choose scanning width based on frequency

An S1G BSS can beacon at either 1 or 2 MHz and the channel
width is unique to a given frequency. Ignore scan channel
width for now and use the allowed channel width.

Signed-off-by: Thomas Pedersen <thomas@adapt-ip.com>
Link: https://lore.kernel.org/r/20200922022818.15855-3-thomas@adapt-ip.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>