scsi: core: Fix passthrough retry counter handling

Passthrough users will set the scsi_cmnd->allowed value and were expecting
up to $allowed retries. The problem is that before:

commit 6aded12b10e0 ("scsi: core: Remove struct scsi_request")

we used to set the retries on the scsi_request then copy them over to
scsi_cmnd->allowed in scsi_setup_scsi_cmnd. With that patch we now set
scsi_cmnd->allowed to 0 in scsi_prepare_cmd and overwrite what the
passthrough user set.

This moves the allowed initialization to after the blk_rq_is_passthrough()
check so it's only done for the non-passthrough path where the ULD
init_command will normally set an allowed value it prefers.

Link: https://lore.kernel.org/r/[e-mail]
Fixes: 6aded12b10e0 ("scsi: core: Remove struct scsi_request")
Reviewed-by: Christoph Hellwig <[e-mail]>
Signed-off-by: Mike Christie <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/scsi_lib.c

···
 	scsi_init_command(sdev, cmd);
 
 	cmd->eh_eflags = 0;
-	cmd->allowed = 0;
 	cmd->prot_type = 0;
 	cmd->prot_flags = 0;
 	cmd->submitter = 0;
···
 			return ret;
 	}
 
+	/* Usually overridden by the ULP */
+	cmd->allowed = 0;
 	memset(cmd->cmnd, 0, sizeof(cmd->cmnd));
 	return scsi_cmd_to_driver(cmd)->init_command(cmd);
 }