dma/ste_dma40: fix erroneous comparison

A small fallout from Vinod's conversions to dma_transfer_direction,
this small comparison was done with a dma_data_direction instead.
Fix it by comparing against the correct enum.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>