drm/i915: Change SDVO fixed mode handling

SDVO is the only connector type currently returning the VBT
fixed mode directly from .get_modes(), everyone else just
adds it to the fixed_modes list and then returns that from
.get_modes(). Adjust SDVO to follow the common behaviour.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220323182935.4701-10-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>