ASoC: hdmi-codec: remove HDMI device unregister

While unregistering the hdmi-codec, the hdmi device list must be
cleaned up. It avoid kernel page fault when registering again the
hdmi-codec.

Signed-off-by: Vincent Abriou <vincent.abriou@st.com>
Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Mark Brown <broonie@kernel.org>