dmaengine: imx-sdma: rename function

Rename sdma_disable_channel_async() after the hook it implements, like
done for all other functions in the SDMA driver.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Link: https://lore.kernel.org/r/20191216105328.15198-8-s.hauer@pengutronix.de


Signed-off-by: Vinod Koul <vkoul@kernel.org>