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>