ste_dma40: Return directly after a failed kmalloc_array()

Return directly after a memory allocation failed in this function
at the beginning.

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>