options: fix -a52drc default value (should be 1)

Commit 3f076c0fb3 ("options: move -a52drc to option struct") from
yesterday left out setting the default value of the option,
effectively changing the default from 1 to 0. Add the missing part to
change it back to 1.

defaultopts.c

@@ -30,6 +30,7 @@ void set_default_mplayer_options(struct MPOpts *opts)
         .video_id = -1,
         .sub_id = -1,
         .playback_speed = 1.,
+        .drc_level = 1.,
         .movie_aspect = -1.,
         .flip = -1,
         .vd_use_slices = 1,