kselftest: alsa: Declare most functions static

This program has only one file so most functions can be static.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Shuah Khan <skhan@linuxfoundation.org>
Reviewed-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20220202150902.19563-2-broonie@kernel.org


Signed-off-by: Takashi Iwai <tiwai@suse.de>