[SCSI] MAINTAINERS: Update zfcp entry

Steffen will take over the zfcp maintainer work. Update the
MAINTAINERS entry accordingly.

Acked-by: Steffen Maier <maier@linux.vnet.ibm.com>
Acked-by: Swen Schillig <swen@vnet.ibm.com>
Signed-off-by: Christof Schmitt <christof.schmitt@de.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>