dma: dw: return DMA_SUCCESS immediately from device_tx_status()

There is no point to go throught the rest of the function if first call to
dma_cookie_status() returned DMA_SUCCESS.

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