drm/edid: Unconfuse preferred timing stuff a bit

For EDID 1.4 the first detailed timing is always preferred,
for older EDIDs there was a feature flag to indicate the same.
While correct, the code setting that up is rather confusing.
Restate it in a slightly more straightforward manner.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220927170006.27855-8-ville.syrjala@linux.intel.com