DMAENGINE: COH 901 318 remove irq counting

This removes the pointless irq counting for the COH 901 318, as
it turns out the hardware will only ever fire one IRQ for a linked
list anyway. In the process also a missing spinlock was introduced.

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