ASoC: Fix leak of rtd in soc_bind_dai_link

If we fail to find a platform we simply return EPROBE_DEFER,
but we have allocated the rtd pointer. All error paths before
soc_add_pcm_runtime need to call soc_free_pcm_runtime first to
avoid leaking the rtd pointer. A suitable error path already
exists and is used else where in the function so simply use that
here as well.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@kernel.org>