qtnfmac: fix STA disconnect procedure

STA does not reconnect to the same AP after disconnect. The reason is
that STA is marked as disconnected in cfg80211 disconnect callback.
This is too early since in this case qtnfmac event handler skips
cfg80211_disconnected call when processing disconnect event from
the card. As a result, wdev is left in an inconsistent state.

Signed-off-by: Sergey Matyukevich <sergey.matyukevich.os@quantenna.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>