watchdog: mei_wdt: request stop on unregister

The MEI bus has a special behavior on suspend it destroys
all the attached devices, this is due to the fact that also
firmware context is not persistent across power flows.

If watchdog on MEI bus is ticking before suspending the firmware
times out and reports that the OS is missing watchdog tick.
Send the stop command to the firmware on watchdog unregistered
to eliminate the false event on suspend.
This does not make the things worse from the user-space perspective
as a user-space should re-open watchdog device after
suspending before this patch.

Cc: <stable@vger.kernel.org>
Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Link: https://lore.kernel.org/r/20210124114938.373885-1-tomas.winkler@intel.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>