drm/edid: reset display info in drm_add_edid_modes() for NULL edid

If a NULL edid gets passed to drm_add_edid_modes(), we should probably
also reset the display 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/2ac1c55f94a08d5e72c0b518d956a11002ec85c1.1651569697.git.jani.nikula@intel.com