MAINTAINERS: normalize Woojung Huh's email address

MAINTAINERS contains a lower-case and upper-case variant of
Woojung Huh' s email address.

Only keep the lower-case variant in MAINTAINERS.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Acked-by: Woojung Huh <woojung.huh@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>