omap: DMA: Init CDAC to zero

The register DMA4_CDAC needs to be initialized to zero
before starting DMA transfer.

Cc: Santosh Shilimkar <santosh.shilimkar@ti.com>
Cc: Govindraj R <govindraj.raja@ti.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Reported-by: S, Venkatraman <svenkatr@ti.com>
Signed-off-by: Manjunatha GK <manjugk@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>