drm/i915/audio: fix compressed_bpp check

The early check for compressed_bpp being zero is too early, as it is hit
also when DSC is not enabled. Move the checks down to where the values
are actually needed. This is a paranoid check for a situation that
should not happen, so we don't really care about handling it gracefully
apart from not oopsing.

Fixes: 48b8b04c ("drm/i915/display: Enable DP Display Audio WA")
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/1750


Cc: Anshuman Gupta <anshuman.gupta@intel.com>
Cc: Uma Shankar <uma.shankar@intel.com>
Reviewed-by: Uma Shankar <uma.shankar@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200420131632.23283-1-jani.nikula@intel.com