dmaengine: dw: Reset DRAIN bit when resume the channel

For Intel iDMA 32-bit the channel can be drained on a suspend.
We need to reset the bit on the resume to return a status quo.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>