mobiclip: fix copyright headers

The Mobiclip related code was based on Mobius (https://github.com/adibsurani/Mobius),
which was based on my original reverse engineering efforts (https://github.com/Gericom/MobiclipDecoder).
This commit adds the appropriate copyright headers on the related files.

Signed-off-by: Florian Nouwt <fnouwt2@gmail.com>

libavcodec/fastaudio.c

@@ -1,5 +1,7 @@
 /*
  * MOFLEX Fast Audio decoder
+ * Copyright (c) 2015-2016 Florian Nouwt
+ * Copyright (c) 2017 Adib Surani
  * Copyright (c) 2020 Paul B Mahol
  *
  * This file is part of FFmpeg.

libavcodec/mobiclip.c

@@ -1,5 +1,6 @@
 /*
  * MobiClip Video decoder
+ * Copyright (c) 2015-2016 Florian Nouwt
  * Copyright (c) 2017 Adib Surani
  * Copyright (c) 2020 Paul B Mahol
  *

libavformat/mods.c

@@ -1,5 +1,7 @@
 /*
  * MODS demuxer
+ * Copyright (c) 2015-2016 Florian Nouwt
+ * Copyright (c) 2017 Adib Surani
  * Copyright (c) 2020 Paul B Mahol
  *
  * This file is part of FFmpeg.

libavformat/moflex.c

@@ -1,5 +1,7 @@
 /*
  * MOFLEX demuxer
+ * Copyright (c) 2015-2016 Florian Nouwt
+ * Copyright (c) 2017 Adib Surani
  * Copyright (c) 2020 Paul B Mahol
  *
  * This file is part of FFmpeg.