leds-clevo-mail: Fix Clevo M5x0V DMI strings

There are more variants of Clevo M5x0V laptops and Positivo Mobile is just one of them.
Another one is UMAX VisionBook 2400WXC. Use only generic Clevo DMI strings to match all
variants.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Bryan Wu <bryan.wu@canonical.com>