There's no need to keep writing registers which don't change value in
omap_dma_start_sg().  Move this into omap_dma_start_desc() and merge
the register updates together.
Acked-by: NTony Lindgren <tony@atomide.com>
Acked-by: NVinod Koul <vinod.koul@intel.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>