ASoC: hdac_hdmi: clean up hdac_ext_device variable names

ASoC: hdac_hdmi: clean up hdac_ext_device variable names

Existing code uses hdac and edev inconsistently to represent
hdac_ext_device structure which creates confusion because hdac
is used even to represent hdac_device. So this patch replaces
all the variable instances of hdac_ext_device with edev.

In the later patch all the variable instances of hdac_device will
be replaced with hdev.

This prepares the code base to remove the usage of hdac_ext_device
data structures done in the subsequent patches.

Signed-off-by: Rakesh Ughreja <rakesh.a.ughreja@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>