Bluetooth: btusb: mediatek: move Bluetooth power off command position

commit ad0c6f60 upstream.

Move MediaTek Bluetooth power off command before releasing
usb ISO interface.

Signed-off-by: Chris Lu <chris.lu@mediatek.com>
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Cc: Fedor Pchelkin <boddah8794@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>