Export snd_soc_runtime_set_dai_fmt() so it can be used in modules.

Fixes: ce64c8b9 ("ASoC: Add helper function for changing the DAI link format")
Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>