DMAENGINE: COH 901 318 fix bytesleft

This makes the function to get the number of bytes left in the
ongoing DMA transaction actually work: the old code did not take
neither lli:s nor queued jobs into account. Also fix a missing
spinlock while we're at it.

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