avfilter/vf_neighbor_opencl: Use AV_PIX_MAX_PLANES

Fix/Robustness/whatever: CID1439575 Out-of-bounds read

Sponsored-by: Sovereign Tech Fund
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavfilter/vf_neighbor_opencl.c

@@ -42,7 +42,7 @@ typedef struct NeighborOpenCLContext {
 
     char *matrix_str[4];
 
-    cl_float threshold[4];
+    cl_float threshold[AV_VIDEO_MAX_PLANES];
     cl_int coordinates;
     cl_mem coord;
 
@@ -93,7 +93,7 @@ static int neighbor_opencl_make_filter_params(AVFilterContext *avctx)
     cl_int cle;
     int i;
 
-    for (i = 0; i < 4; i++) {
+    for (i = 0; i < AV_VIDEO_MAX_PLANES; i++) {
         ctx->threshold[i] /= 255.0;
     }