tools headers UAPI: Sync sound/asound.h with the kernel sources

To pick up the changes in:

  5aec579e

 ("ALSA: uapi: Fix a C++ style comment in asound.h")

That is just changing a // style comment to /* */.

This silences this perf build warning:

  Warning: Kernel ABI header at 'tools/include/uapi/sound/asound.h' differs from latest version at 'include/uapi/sound/asound.h'
  diff -u tools/include/uapi/sound/asound.h include/uapi/sound/asound.h

Cc: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>