dmaengine: ste_dma40: Rectify incorrect configuration validation checking

If we compare an event's group (dev_type / 16) with STEDMA40_DEV_DST_MEMORY
(-1), the only way we'd obtain a positive result is if we passed -16 as a
device type, which is unfeasible. Instead, it would be much more sane to
compare STEDMA40_DEV_DST_MEMORY against the raw dev_type in order to expect
the expected result.

Acked-by: Vinod Koul <vinod.koul@intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>