avfilter: Add missing emms_c when needed

Arch specific calls should have an emms_c following to keep the cpu
state consistent.

Reported-By: wm4
CC: libav-stable@libav.org
(cherry picked from commit e995cf1bcc)

libavfilter/af_volume.c

@@ -282,6 +282,8 @@ static int filter_frame(AVFilterLink *inlink, AVFilterBufferRef *buf)
         }
     }
 
+    emms_c();
+
     if (buf != out_buf)
         avfilter_unref_buffer(buf);
 

libavfilter/vf_gradfun.c

@@ -117,6 +117,7 @@ static void filter(GradFunContext *ctx, uint8_t *dst, uint8_t *src, int width, i
         ctx->filter_line(dst + y * dst_linesize, src + y * src_linesize, dc - r / 2, width, thresh, dither[y & 7]);
         if (++y >= height) break;
     }
+    emms_c();
 }
 
 static av_cold int init(AVFilterContext *ctx, const char *args)

libavfilter/vf_hqdn3d.c

@@ -155,6 +155,7 @@ static void denoise_depth(HQDN3DContext *hqdn3d,
     else
         denoise_temporal(src, dst, frame_ant,
                          w, h, sstride, dstride, temporal, depth);
+    emms_c();
 }
 
 #define denoise(...) \