ath6kl: remove a workaround from ath6kl_cfg80211_stop()

There's a workaround in ath6kl_cfg80211_stop() which emits disconnected
even when sme_state was disconnected. This is legacy from the old
staging driver and I can't repoduce the old problem anymore. I assume the
bug got fixed while the driver was cleaned up so let's get
rid of the hack.

This makes it possible to call ath6kl_cfg80211_stop from ath6kl_close()
which happens in a followup patch.

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