dmaengine: imx-sdma: Correct formatting issue and provide 2 new descriptions

dmaengine: imx-sdma: Correct formatting issue and provide 2 new descriptions

Fixes the following W=1 kernel build warning(s):

 drivers/dma/imx-sdma.c:383: warning: Function parameter or member 'slave_config' not described in 'sdma_channel'
 drivers/dma/imx-sdma.c:383: warning: Function parameter or member 'context_loaded' not described in 'sdma_channel'
 drivers/dma/imx-sdma.c:383: warning: Function parameter or member 'terminate_worker' not described in 'sdma_channel'

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Pengutronix Kernel Team <kernel@pengutronix.de>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: NXP Linux Team <linux-imx@nxp.com>
Link: https://lore.kernel.org/r/20200714111546.1755231-12-lee.jones@linaro.org
Signed-off-by: Vinod Koul <vkoul@kernel.org>