wifi: mac80211: don't unreserve never reserved chanctx

wifi: mac80211: don't unreserve never reserved chanctx

If a link has no chanctx, indicating it is an inactive link
that we tracked CSA for, then attempting to unreserve the
reserved chanctx will throw a warning and fail, since there
never was a reserved chanctx. Skip the unreserve.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Miri Korenblit <miriam.rachel.korenblit@intel.com>
Link: https://patch.msgid.link/20250709233537.022192f4b1ae.Ib58156ac13e674a9f4d714735be0764a244c0aae@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>