DMAENGINE: ste_dma40: No need reading, masking and setting a set register

Removes an unnecessary register read and a few lines of code.

Signed-off-by: Jonas Aaberg <jonas.aberg@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>