avfilter/vf_atadenoise: do not abort if user specified invalid size

Update documentation with new size default.
Signed-off-by: Paul B Mahol <onemda@gmail.com>

doc/filters.texi

@@ -5247,7 +5247,7 @@ Threshold A is designed to react on abrupt changes in the input signal and
 threshold B is designed to react on continuous changes in the input signal.
 
 @item s
-Set number of frames filter will use for averaging. Default is 33. Must be odd
+Set number of frames filter will use for averaging. Default is 9. Must be odd
 number in range [5, 129].
 
 @item p

libavfilter/vf_atadenoise.c

@@ -112,8 +112,8 @@ static av_cold int init(AVFilterContext *ctx)
     ATADenoiseContext *s = ctx->priv;
 
     if (!(s->size & 1)) {
-        av_log(ctx, AV_LOG_ERROR, "size %d is invalid. Must be an odd value.\n", s->size);
-        return AVERROR(EINVAL);
+        av_log(ctx, AV_LOG_WARNING, "size %d is invalid. Must be an odd value, setting it to %d.\n", s->size, s->size|1);
+        s->size |= 1;
     }
     s->mid = s->size / 2 + 1;