cfg80211: fix boundary value in ieee80211_frequency_to_channel()

The boundary value used for the 6G band was incorrect as it would
result in invalid 6G channel number for certain frequencies.

Reported-by: Amar Singhal <asinghal@codeaurora.org>
Signed-off-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Link: https://lore.kernel.org/r/1567510772-24263-1-git-send-email-arend.vanspriel@broadcom.com


Signed-off-by: Johannes Berg <johannes.berg@intel.com>