ALSA: Fix initiailization of user-space controls

Fix an assertion when accessing a user-defined control due to lack of
initialization (appears only when CONFIG_SND_DEBUg is enabled).

  ALSA sound/core/control.c:660: BUG? (info->access == 0)

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