dmaengine: dw-edma: Skip cleanup procedure if no private data found

DW eDMA driver private data is preserved in the passed DW eDMA chip info
structure. If either probe procedure failed or for some reason the passed
info object doesn't have private data pointer initialized we need to halt
the DMA device cleanup procedure in order to prevent possible system
crashes.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Tested-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Acked-By: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>