scsi: iscsi: MAINTAINERS: Add Mike Christie as co-maintainer

I've been doing a lot of iscsi patches because Oracle is paying me to work
on iSCSI again. It was supposed to be temp assignment, but my co-worker
that was working on iscsi moved to a new group so it looks like I'm back on
this code again. After talking to Chris and Lee this patch adds me back as
co-maintainer, so I can help them and people remember to cc me on issues.

Link: https://lore.kernel.org/r/20220408001314.5014-11-michael.christie@oracle.com
Tested-by: Manish Rangankar <mrangankar@marvell.com>
Acked-by: Lee Duncan <lduncan@suse.com>
Acked-by: Chris Leech <cleech@redhat.com>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>