dmaengine: cppi41: fix cppi41_dma_tx_status() logic

It makes sense to set residue when channel is in progress. Otherwise it
should be 0 since transfer is completed. Meanwhile this patch doesn't
prevent to set residue value anyway.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>