avcodec/mjpegenc_common: Restore removed copyright statements

These where removed by  libav while spliting the file in adcb8392

See: de6d9b64
See: 723106b2Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/mjpegenc_common.c

 /*
  * lossless JPEG shared bits
+ * Copyright (c) 2000, 2001 Fabrice Bellard
+ * Copyright (c) 2003 Alex Beregszaszi
  *
  * This file is part of FFmpeg.
  *