MAINTAINERS: EP93XX: Update maintainership

As agreed with Ryan, change the maintainership.

Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Acked-by: Ryan Mallon <rmallon@gmail.com>
Acked-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Olof Johansson <olof@lixom.net>