dma: pl330: Set residue_granularity

The pl330 driver currently does not support residue reporting, so set the
residue granularity to DMA_RESIDUE_GRANULARITY_DESCRIPTOR.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Mark Brown <broonie@linaro.org>