MAINTAINERS: Add vfio-ccw maintainers

Add Cornelia Huck and myself as the vfio-ccw driver maintainers.

Signed-off-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>
Message-Id: <20170317031743.40128-17-bjsdjshi@linux.vnet.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>