lavc/hevc_ps: Use correct pix_fmt for 12bit 4:0:0.

Fixes part of ticket #5544.

libavcodec/hevc_ps.c

@@ -796,7 +796,7 @@ static int map_pixel_format(AVCodecContext *avctx, HEVCSPS *sps)
         if (sps->chroma_format_idc == 3) sps->pix_fmt = AV_PIX_FMT_YUV444P10;
         break;
     case 12:
-        if (sps->chroma_format_idc == 0) sps->pix_fmt = AV_PIX_FMT_GRAY16;
+        if (sps->chroma_format_idc == 0) sps->pix_fmt = AV_PIX_FMT_GRAY12;
         if (sps->chroma_format_idc == 1) sps->pix_fmt = AV_PIX_FMT_YUV420P12;
         if (sps->chroma_format_idc == 2) sps->pix_fmt = AV_PIX_FMT_YUV422P12;
         if (sps->chroma_format_idc == 3) sps->pix_fmt = AV_PIX_FMT_YUV444P12;