dma/imx-sdma: let sdma_run_channel call sdma_enable_channel

Let all enable channel code call sdma_enable_channel.

Signed-off-by: Richard Zhao <richard.zhao@linaro.org>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>