xhci: cleanup virtual endoint structure, remove stopped_stream

Get rid of stopped_stream member in virtual endpoint structure as
it is only used in one case when cleaning a halted endpoint.

Pass it as function parameter instead.

No functional changes

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>