scsi: mpi3mr: Fix duplicate device entries when scanning through sysfs

When scanning devices through the 'scan' attribute in sysfs, the user will
observe duplicate device entries in lsscsi command output.

Set the shost's max_channel to zero to avoid this.

Link: https://lore.kernel.org/r/20211014055425.30719-1-sreekanth.reddy@broadcom.com


Fixes: 824a1566 ("scsi: mpi3mr: Base driver code")
Signed-off-by: Sreekanth Reddy <sreekanth.reddy@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>