dmaengine: ste_dma40: Move rev error-check up to revision acquisition

At the moment we fetch the hardware revision, then do some stuff, then
check whether the revision is correct and return in error if it's not.
Well we may as well check it as soon as we know what it is, so let's
move the check right up underneath where we acquire the version.

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