mmc: Add maintainers for TI OMAP MMC interface

Carlos Aguiar and Anderson Briglia are interested in making sure
the driver works for existing boards as they have access to them,
and Syed Khasim can make it work for new omaps (2430, 3430).

Signed-off-by: Syed Khasim <x0khasim@ti.com>
Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>