avcodec/ac3enc: Use specific error code in validate_float_option()

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/ac3enc.c

@@ -1800,7 +1800,7 @@ static int validate_float_option(float v, const float *v_list, int v_list_size)
             break;
     }
     if (i == v_list_size)
-        return -1;
+        return AVERROR(EINVAL);
 
     return i;
 }