ste_dma40: One check less in d40_prep_sg() after error detection

* Adjust jump targets according to the Linux coding style convention.

* Delete a repeated check which became unnecessary with this refactoring.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>