dma: tegra20-apb-dma: remove unnecessary assignment

There is no need to assign 0 to residue, because dma_cookie_status() does this
for us.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Acked-by: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>