Unify amongst sink drivers how the AUX ring buffer head is communicated
to user space.  That way the same algorithm in user space can be used to
determine where the latest data is and how much of it to access.
Signed-off-by: NMathieu Poirier <mathieu.poirier@linaro.org>
Reviewed-by: NSuzuki K Poulose <suzuki.poulose@arm.com>
Tested-by: NLeo Yan <leo.yan@linaro.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>