dmaengine: bcm2835: set residue_granularity field

bcm2835-dma supports residue reporting at burst level but didn't report
this via the residue_granularity field.

See also:
https://github.com/raspberrypi/linux/commit/b015555327afa402f70ddc86e3632f59df1cd9d7


for the downstream patch.

Signed-off-by: Matthias Reichl <hias@horus.com>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>