usb/hcd: Ensure scatter-gather is not used for isoc transfers

We don't support sg for isoc transfers, enforce this.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>