dmaengine: at_hdmac: use dma_address to program DMA hardware

In atc_prep_slave_sg() function we use dma_address field of scatterlist with
sg_dma_address() macro instead of sg_phys(). DMA address is already computed
by dma_map_sg() or another mapping function in calling driver.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>