ARM: u300: regulator: add MODULE_LICENSE()

The missing license showed up as a randconfig warning now, no idea
why we never saw that earlier.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Olof Johansson <olof@lixom.net>