wifi: mac80211: chan: chandef is non-NULL for reserved

The last caller of this with a NULL argument was related to
the non-chanctx code, so we can now remove this odd logic.

Reviewed-by: Miriam Rachel Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://msgid.link/20240129194108.bad8ec1e76c8.I12287452f42c54baf75821e75491cf6d021af20a@changeid


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