DMAENGINE: DMA40 fix for allocation of logical channel 0

Fix for allocation failure of logical channel when event line
happens to be number 0.

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