scsi/sg: don't grab scsi host module reference

In order to prevent request_queue to be freed before cleaning up
blktrace debugfs entries, commit db59133e9279 ("scsi: sg: fix blktrace
debugfs entries leakage") use scsi_device_get(), however,
scsi_device_get() will also grab scsi module reference and scsi module
can't be removed.

It's reported that blktests can't unload scsi_debug after block/001:

blktests (master) # ./check block
block/001 (stress device hotplugging) [failed]
+++ /root/blktests/results/nodev/block/001.out.bad 2023-06-19
Running block/001
Stressing sd
+modprobe: FATAL: Module scsi_debug is in use.

Fix this problem by grabbing request_queue reference directly, so that
scsi host module can still be unloaded while request_queue will be
pinged by sg device.

Reported-by: Chaitanya Kulkarni <[e-mail]>
Link: https://lore.kernel.org/all/[e-mail]/
Fixes: db59133e9279 ("scsi: sg: fix blktrace debugfs entries leakage")
Signed-off-by: Yu Kuai <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jens Axboe <[e-mail]>

drivers/scsi/sg.c

···
 	int error;
 	unsigned long iflags;
 
-	error = scsi_device_get(scsidp);
+	error = blk_get_queue(scsidp->request_queue);
 	if (error)
 		return error;
 
···
 out:
 	if (cdev)
 		cdev_del(cdev);
-	scsi_device_put(scsidp);
+	blk_put_queue(scsidp->request_queue);
 	return error;
 }
 
···
 	 */
 
 	blk_trace_remove(q);
-	scsi_device_put(sdp->device);
+	blk_put_queue(q);
 
 	write_lock_irqsave(&sg_index_lock, flags);
 	idr_remove(&sg_index_idr, sdp->index);