dmaengine: ste_dma40: fix pm runtime ref counting

The pm runtime reference counting of the driver is broken for the case
when there is more than one transfer queued, leading to the device being
runtime suspend while active.  Fix it.

Signed-off-by: Rabin Vincent <rabin.vincent@stericsson.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Cc: stable@vger.kernel.org
Signed-off-by: Vinod Koul <vinod.koul@intel.com>