soc: ti: knav_dma: Fix a kernel function doc formatting issue

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

 drivers/soc/ti/knav_dma.c:507: warning: Function parameter or member 'channel' not described in 'knav_dma_close_channel'

Cc: Santosh Shilimkar <ssantosh@kernel.org>
Cc: Sandeep Nair <sandeep_n@ti.com>
Cc: Cyril Chemparathy <cyril@ti.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>