scsi: iscsi: Fix shost->max_id use

stable inclusion
from linux-4.19.198
commit 693e09c3be3cc130320036861c0d249da03bf1be

--------------------------------

[ Upstream commit bdd4aad7 ]

The iscsi offload drivers are setting the shost->max_id to the max number
of sessions they support. The problem is that max_id is not the max number
of targets but the highest identifier the targets can have. To use it to
limit the number of targets we need to set it to max sessions - 1, or we
can end up with a session we might not have preallocated resources for.

Link: https://lore.kernel.org/r/20210525181821.7617-15-michael.christie@oracle.com


Reviewed-by: Lee Duncan <lduncan@suse.com>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>