mei: fix undefined wd symbols when MEI_ME is not set

Currently watchdog client is compiled with MEI and not
with MEI_ME

Fixes error:
When CONFIG_WATCHDOG is not enabled:

ERROR: "watchdog_unregister_device" [drivers/misc/mei/mei.ko] undefined!
ERROR: "watchdog_register_device" [drivers/misc/mei/mei.ko] undefined

Reported-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>