AP: Fix regression in frequency check for a usable EDMG channel

AP: Fix regression in frequency check for a usable EDMG channel

Commit 5f9b4afd ("Use frequency in HT/VHT validation steps done before
starting AP") modified hostapd_is_usable_edmg() to use freq instead of
channel numbers. Unfortunately, it did not convert the frequency
calculation correctly and this broke EDMG functionality.

Fix the frequency calculation so that EDMG channel 9 works again.

Fixes: 5f9b4afdfaf5 ("Use frequency in HT/VHT validation steps done before starting AP")
Signed-off-by: Hrishikesh Vidwans <hvidwans@codeaurora.org>