dma/ste_dma40: Fixup clock usage during probe

Fixup some errorhandling for clocks during probe and make sure
to use clk_prepare as well as clk_enable.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>