avcodec/videotoolboxenc: fix align issue

bool a53_cc is accessed as int:
src/libavutil/opt.c:129:9: runtime error: store to misaligned
address 0x7fbf454121a3 for type 'int', which requires 4 byte alignment
Signed-off-by: NRick Kern <kernrj@gmail.com>

libavcodec/videotoolboxenc.c

@@ -226,7 +226,9 @@ typedef struct VTEncContext {
     bool flushing;
     bool has_b_frames;
     bool warned_color_range;
-    bool a53_cc;
+
+    /* can't be bool type since AVOption will access it as int */
+    int a53_cc;
 } VTEncContext;
 
 static int vtenc_populate_extradata(AVCodecContext   *avctx,