codec: twolame: return VLC_EGENERIC

...instead of -VLC_EGENERIC, leading to an overflow.

../../modules/codec/twolame.c: In function ‘OpenEncoder’:
../../modules/codec/twolame.c:236:16: warning: integer overflow in expression ‘-2147483648’ of type ‘int’ results in ‘-2147483648’ [-Woverflow]
  236 |         return -VLC_EGENERIC;
      |                ^

modules/codec/twolame.c

@@ -233,7 +233,7 @@ static int OpenEncoder( vlc_object_t *p_this )
     if ( twolame_init_params( p_sys->p_twolame ) )
     {
         msg_Err( p_enc, "twolame initialization failed" );
-        return -VLC_EGENERIC;
+        return VLC_EGENERIC;
     }
 
     p_enc->pf_encode_audio = Encode;