MAINTAINERS - Add an entry for the input MT protocol

This patch adds a maintainer for the input multitouch (MT) protocol,
such that get_maintainer.pl selects it whenever an MT event is present
in the patch.

Signed-off-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>