[ALSA] unexport snd_ctl_elem_{read,write}

snd_ctl_elem_{read,write} no longer have any modular users

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>