Bluetooth: btmrvl: wait for HOST_SLEEP_ENABLE event in suspend
After BT_CMD_HOST_SLEEP_ENABLE command finishes, driver should
wait until getting BT_EVENT_HOST_SLEEP_ENABLE event to complete
suspend procedure.
Without this patch the suspend handler would return success
earlier. By the time when the BT_EVENT_HOST_SLEEP_ENABLE event
comes in the controller driver could have already turned off the
bus clock. This causes kernel crash or system reboot eventually.