DMAENGINE: COH 901 318 lli sg offset fix

This makes the COH 901 318 respect the scatter offset field by using
the sg_phys() rather than the sg_dma_address() so we get a pointer
to the actual data we want to send rather than the beginning of the
buffer. Also initialize the lli:s a bit more thoroughly.

Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>