Bluetooth: hci_sync: Don't wait peer's reply when powering off

Currently, when we initiate disconnection, we will wait for the peer's
reply unless when we are suspending, where we fire and forget the
disconnect request.

A similar case is when adapter is powering off. However, we still wait
for the peer's reply in this case. Therefore, if the peer is
unresponsive, the command will time out and the power off sequence
will fail, causing "bluetooth powered on by itself" to users.

This patch makes the host doesn't wait for the peer's reply when the
disconnection reason is powering off.

Signed-off-by: Archie Pusaka <apusaka@chromium.org>
Reviewed-by: Abhishek Pandit-Subedi <abhishekpandit@google.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>