drm/i915/display: return earlier from intel_modeset_init() without display

!HAS_DISPLAY() implies !HAS_OVERLAY(), skipping overlay setup anyway, so
return earlier from intel_modeset_init() for clarity.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: José Roberto de Souza <jose.souza@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201106225531.920641-4-lucas.demarchi@intel.com