ASoC: SOF: Clean up sof_ipc_flood_dfs_write()

This function doesn't support partial writes so using
simple_write_to_buffer() doesn't really make sense.  It's better to
just use copy_from_user().

Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Acked-by: Peter Ujfalusi <peter.ujfalusi@linux.intel.com>
Link: https://msgid.link/r/a35dded2-392b-4ccb-9dbb-d782ac9b6547@moroto.mountain


Signed-off-by: Mark Brown <broonie@kernel.org>