usbdevfs: Fix broken scatter-gather transfer

The handling of large output bulk transfers is broken; the same user
page is read over and over again. Fixed with this patch.

Cc: stable <stable@vger.kernel.org>
Acked-by: NPeter Stuge <peter@stuge.se>
Acked-by: NHans de Goede <hdegoede@redhat.com>
Acked-by: NAlan Stern <stern@rowland.harvard.edu>
Signed-off-by: NHenrik Rydberg <rydberg@euromail.se>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/devio.c

@@ -1348,6 +1348,7 @@ static int proc_do_submiturb(struct dev_state *ps, struct usbdevfs_urb *uurb,
 					ret = -EFAULT;
 					goto error;
 				}
+				uurb->buffer += u;
 			}
 			totlen -= u;
 		}