wifi: mac80211: initialize SMPS mode correctly

The SMPS mode is currently re-initialized too late, since
ieee80211_prep_channel() can be called again after we've
already done ieee80211_setup_assoc_link(), in case there's
some override of the channel configuration. Fix this.

Link: https://msgid.link/20240129195405.d6d74508be18.I0a7303b1ce4d8e5436011951ab624372a445c069@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>