ath6kl: don't use cfg80211_scan_request after cfg80211_scan_done()

Use of cfg80211_scan_request is not valid after calling cfg80211_scan_done()
but ath6kl_cfg80211_scan_complete_event() was doing exactly that. Change
the function to call cfg80211_scan_done() last.

This was found during code review, I didn't see any visible problems
due to this bug.

Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>