wil6210: ignore firmware failure to gracefully stop AP

upon cfg80211_stop_ap, a graceful AP shutdown is requested from firmware
followed by firmware reset.
In case graceful request failed, error was returned to cfg80211.

The change is to return success in this scenario, because firmware
reset will anyhow shutdown the AP.

Signed-off-by: Dedy Lansky <qca_dlansky@qca.qualcomm.com>
Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>