ASoC: Remove name_prefix unset during DAI link init hack

Before we had card level support for DAPM and controls machine drivers would
register their controls and DAPM elements with the CODEC. This required us to
temporarily unset the name_prefix of a CODEC during the rtd init callback to
avoid the machine level controls getting the CODEC's prefix. Now that all
machine drivers properly register their machine level controls and DAPM elements
with the card rather than with the CODEC we can drop the hack that sets the
CODEC's name_prefix to NULL while calling the DAI link or AUX dev init callback.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>