scsi: need to reset unprep_rq_fn in sd_remove

This is for block's for-2.6.36.

We need to reset q->unprep_rq_fn in sd_remove. Otherwise we hit kernel
oops if we access to a scsi disk device via sg after removing scsi
disk module.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

drivers/scsi/sd.c

@@ -2384,6 +2384,7 @@ static int sd_remove(struct device *dev)
 	async_synchronize_full();
 	sdkp = dev_get_drvdata(dev);
 	blk_queue_prep_rq(sdkp->device->request_queue, scsi_prep_fn);
+	blk_queue_unprep_rq(sdkp->device->request_queue, NULL);
 	device_del(&sdkp->dev);
 	del_gendisk(sdkp->disk);
 	sd_shutdown(dev);