[PATCH] USB: gadget zero and dma-coherent buffers

This makes sure that the correct length is reported when freeing
a dma-coherent buffer; some platforms complain if that's wrong.
It also makes two parameters readonly in sysfs, as they're not
safe to change while tests are running.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>