ASoC: Intel: bytcht_es8316: Minor refactoring

Some minor refactoring:
1) Group the code setting the card dev and prive pointers together with
   registering the card
2) Properly put the comment about registering the card at the place where
   we actually register the card and add a new comment for getting the clk
3) Add a struct device *dev helper variable (this will be used more in
   follow up commits)
4) Reword error message to have the same "foo failed: %d" wording as others

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>