MAINTAINERS: vfio-ccw: Remove myself as the maintainer

I will not be able to continue with my maintainership responsibilities
going forward, so remove myself as the maintainer.

Signed-off-by: Farhan Ali <alifm@linux.ibm.com>
Acked-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>