avcodec/h264: use subsample factors of the used pixel format

Fixes out of array read
Fixes: 1cb91c36c4e55463f14aacb9bdf55b38-asan_heap-oob_106cbce_5617_cov_11212800_h264_mmx_chroma_intra_lf.mp4
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/h264.c

@@ -5133,6 +5133,7 @@ static int get_consumed_bytes(int pos, int buf_size)
 static int output_frame(H264Context *h, AVFrame *dst, Picture *srcp)
 {
     AVFrame *src = &srcp->f;
+    const AVPixFmtDescriptor *desc = av_pix_fmt_desc_get(src->format);
     int i;
     int ret = av_frame_ref(dst, src);
     if (ret < 0)
@@ -5143,9 +5144,9 @@ static int output_frame(H264Context *h, AVFrame *dst, Picture *srcp)
     if (!srcp->crop)
         return 0;
 
-    for (i = 0; i < 3; i++) {
-        int hshift = (i > 0) ? h->chroma_x_shift : 0;
-        int vshift = (i > 0) ? h->chroma_y_shift : 0;
+    for (i = 0; i < desc->nb_components; i++) {
+        int hshift = (i > 0) ? desc->log2_chroma_w : 0;
+        int vshift = (i > 0) ? desc->log2_chroma_h : 0;
         int off    = ((srcp->crop_left >> hshift) << h->pixel_shift) +
                       (srcp->crop_top  >> vshift) * dst->linesize[i];
         dst->data[i] += off;