dmaengine: imx-sdma: Check for clk_enable() errors

clk_enable() may fail, so we should better check the return value and
propagate it in the case of error.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>