cfg80211: fix 6 GHz frequencies to kHz

The updates to change to kHz frequencies and the 6 GHz
additions evidently overlapped (or rather, I didn't see
it when applying the latter), so the 6 GHz is broken.
Fix this.

Fixes: 934f4c7d ("cfg80211: express channels with a KHz component")
Link: https://lore.kernel.org/r/20200529140425.1bf824f6911b.I4a1174916b8f5965af4366999eb9ffc7a0347470@changeid


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