[ALSA] make sound/core/control.c:snd_ctl_new() static

Now that everyone uses snd_ctl_new1() and noone is using snd_ctl_new()
anymore, we can make it static.

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