ASoC: Blackfin TDM: fix missed snd_soc_dai_get_drvdata update

One spot was missed in this driver when converting from
snd_soc_dai.private_data to snd_soc_dai_get_drvdata.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Cc: stable@kernel.org