block: fix bogus EFAULT error from SG_IO ioctl

Whenever blk_fill_sghdr_rq fails, its errno code is ignored and changed to
EFAULT.  This can cause very confusing errors:

  $ sg_persist -k /dev/sda
  persistent reservation in: pass through os error: Bad address

The fix is trivial, just propagate the return value from
blk_fill_sghdr_rq.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

block/scsi_ioctl.c

@@ -326,8 +326,8 @@ static int sg_io(struct request_queue *q, struct gendisk *bd_disk,
 			goto out_put_request;
 	}
 
-	ret = -EFAULT;
+	ret = blk_fill_sghdr_rq(q, rq, hdr, mode);
-	if (blk_fill_sghdr_rq(q, rq, hdr, mode))
+	if (ret < 0)
 		goto out_free_cdb;
 
 	ret = 0;