sound: Update some LICENSE headers

The following commits introduced substantial changes to pcm/dsp.c,
pcm/sndstat.c and pcm/sound.c.

9da3b645db ("sound: Move
sndstat_prepare_pcm() to pcm/sndstat.c and remove
sndstat_entry->handler")
e8c0d15a64 ("sound: Get rid of snd_clone
and use DEVFS_CDEVPRIV(9)")

Sponsored by:	The FreeBSD Foundation
MFC after:	1 week
Reviewed by:	markj
Differential Revision:	https://reviews.freebsd.org/D44757

sys/dev/sound/pcm/dsp.c

@@ -5,6 +5,10 @@
  * Portions Copyright (c) Ryan Beasley <ryan.beasley@gmail.com> - GSoC 2006
  * Copyright (c) 1999 Cameron Grant <cg@FreeBSD.org>
  * All rights reserved.
+ * Copyright (c) 2024 The FreeBSD Foundation
+ *
+ * Portions of this software were developed by Christos Margiolis
+ * <christos@FreeBSD.org> under sponsorship from the FreeBSD Foundation.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions

sys/dev/sound/pcm/sndstat.c

@@ -5,6 +5,10 @@
  * Copyright (c) 2001 Cameron Grant <cg@FreeBSD.org>
  * Copyright (c) 2020 The FreeBSD Foundation
  * All rights reserved.
+ * Copyright (c) 2024 The FreeBSD Foundation
+ *
+ * Portions of this software were developed by Christos Margiolis
+ * <christos@FreeBSD.org> under sponsorship from the FreeBSD Foundation.
  *
  * Portions of this software were developed by Ka Ho Ng
  * under sponsorship from the FreeBSD Foundation.

sys/dev/sound/pcm/sound.c

@@ -6,6 +6,10 @@
  * Copyright (c) 1999 Cameron Grant <cg@FreeBSD.org>
  * Copyright (c) 1997 Luigi Rizzo
  * All rights reserved.
+ * Copyright (c) 2024 The FreeBSD Foundation
+ *
+ * Portions of this software were developed by Christos Margiolis
+ * <christos@FreeBSD.org> under sponsorship from the FreeBSD Foundation.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions