drm/edid: convert drm_edid_to_speaker_allocation() to use cea db iter

Use the cea db iterator for speaker allocation. We'll still stop at the
first speaker data block, but not at the first CTA extension if that
doesn't have the info.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/0b9e7f136854055a14b826097160fe0b43b9f3d1.1651569697.git.jani.nikula@intel.com