cfg80211: simplify cfg80211_chandef_valid()

cfg80211: simplify cfg80211_chandef_valid()

There are a lot of duplicate checks in this function to
check the delta between the control channel and CF1.
With the addition of 320 MHz, this will become even more.
Simplify the code so that the common checks are done
only once for multiple bandwidths.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20211129152938.2d0240b07f11.I759e8e990f5386ba2b56ffb2488a8d4e16e22c1b@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>