drm/i915/audio: simplify, don't mask out in all branches

Lift the masking outside of the if branches. No functional changes.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/a87fd5e66b52c4d52a568888e1b8037841786fd2.1620115982.git.jani.nikula@intel.com