leds: Add mail LED support for "Clevo D400P"

The leds-clevo-mail module also works with model "Clevo D400P",
add this model to the white list.

Signed-off-by: Mrton Nmeth <nm127@freemail.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Richard Purdie <rpurdie@rpsys.net>