ath10k: update vdev ps state on start

Psmode can be forcefully enabled when vdev isn't
started. It isn't guaranteed that mac80211 will
re-issue psmode setting after vdev is started
unless actual bss_conf.ps value has changed.

Even if this doesn't fix any problems now it may
prevent future breakage.

Signed-off-by: Michal Kazior <michal.kazior@tieto.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>