lavc: fix wrong example code in avcodec_find_best_pix_fmt() docs

A pix_fmt_mask is obtained by bitwise or-ing two pixel format bits,
rather than doing a logical or.
Signed-off-by: Stefano Sabatini <stefano.sabatini-lala@poste.it>

libavcodec/avcodec.h

@@ -3503,7 +3503,7 @@ int avcodec_get_pix_fmt_loss(enum PixelFormat dst_pix_fmt, enum PixelFormat src_
  *
  * @code
  * src_pix_fmt = PIX_FMT_YUV420P;
- * pix_fmt_mask = (1 << PIX_FMT_YUV422P) || (1 << PIX_FMT_RGB24);
+ * pix_fmt_mask = (1 << PIX_FMT_YUV422P) | (1 << PIX_FMT_RGB24);
  * dst_pix_fmt = avcodec_find_best_pix_fmt(pix_fmt_mask, src_pix_fmt, alpha, &loss);
  * @endcode
  *