clk_prepare_enable() may fail, so let's check its return value and propagate it
in the case of error.

While at it, rename 'out_free_dma' to 'out_disable_clk' so that it can properly
describe its purpose.
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>
Acked-by: NMarek Vasut <marex@denx.de>
Signed-off-by: NMark Brown <broonie@linaro.org>