scsi: sg: Fix checking return value of blk_get_queue()

Commit fcaa174a9c99 ("scsi/sg: don't grab scsi host module reference") make
a mess how blk_get_queue() is called, blk_get_queue() returns true on
success while the caller expects it returns 0 on success.

Fix this problem and also add a corresponding error message on failure.

Fixes: fcaa174a9c99 ("scsi/sg: don't grab scsi host module reference")
Reported-by: Marc Hartmayer <[e-mail]>
Closes: https://lore.kernel.org/all/[e-mail]/
Signed-off-by: Yu Kuai <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Tested-by: Shin'ichiro Kawasaki <[e-mail]>
Tested-by: Marc Hartmayer <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Marc Hartmayer <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/scsi/sg.c

···
 	int error;
 	unsigned long iflags;
 
-	error = blk_get_queue(scsidp->request_queue);
-	if (error)
-		return error;
+	if (!blk_get_queue(scsidp->request_queue)) {
+		pr_warn("%s: get scsi_device queue failed\n", __func__);
+		return -ENODEV;
+	}
 
 	error = -ENOMEM;
 	cdev = cdev_alloc();