Use per-descriptor 'len' field to keep track of the remaining bytes
instead. This goes on the direction of eventually removing the
'internal' structure.
Signed-off-by: Javier Martin <javier.martin@vista-silicon.com> Acked-by: Sascha Hauer <s.hauer@pengutronix.de> Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>