mmc: MAINTAINERS: change omap_hsmmc maintainence to orphan

Update the OMAP HSMMC entry from the MAINTAINERS file as I will
no longer be able to maintain this driver.

Signed-off-by: Madhusudhan Chikkature <madhu.cr@ti.com>
[khilman@ti.com: change to Orphan rather than complete removal]
Signed-off-by: Kevin Hilman <khilman@ti.com>
Acked-by: Venkatraman S <svenkatr@ti.com>
Signed-off-by: Chris Ball <cjb@laptop.org>