wifi: mac80211: adding missing drv_mgd_complete_tx() call

There's a call to drv_mgd_prepare_tx() and so there should
be one to drv_mgd_complete_tx(), but on this path it's not.
Add it.

Link: https://msgid.link/20240131164824.2f0922a514e1.I5aac89b93bcead88c374187d70cad0599d29d2c8@changeid


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