avfilter/vf_histogram: fix bug in checking pixel format flags

Signed-off-by: Paul B Mahol <onemda@gmail.com>

libavfilter/vf_histogram.c

@@ -150,7 +150,7 @@ static int query_formats(AVFilterContext *ctx)
         rgb = desc->flags & AV_PIX_FMT_FLAG_RGB;
         for (i = 1; i < avff->nb_formats; i++) {
             desc = av_pix_fmt_desc_get(avff->formats[i]);
-            if (rgb != desc->flags & AV_PIX_FMT_FLAG_RGB)
+            if (rgb != (desc->flags & AV_PIX_FMT_FLAG_RGB))
                 return AVERROR(EAGAIN);
         }