usb: usbfs: only account once for mmap()'ed usb memory usage

Memory usage for USB memory allocated via mmap() is already accounted
for at mmap() time; no need to account for it again at submiturb time.

Signed-off-by: Gavin Li <git@thegavinli.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Link: https://lore.kernel.org/r/20190814212924.10381-1-gavinli@thegavinli.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/devio.c

@@ -1664,7 +1664,8 @@ static int proc_do_submiturb(struct usb_dev_state *ps, struct usbdevfs_urb *uurb
 	if (as->usbm)
 		num_sgs = 0;
 
-	u += sizeof(struct async) + sizeof(struct urb) + uurb->buffer_length +
+	u += sizeof(struct async) + sizeof(struct urb) +
+	     (as->usbm ? 0 : uurb->buffer_length) +
 	     num_sgs * sizeof(struct scatterlist);
 	ret = usbfs_increase_memory_usage(u);
 	if (ret)