sound: snd_ctl_elem_add: fix value count check

Make sure that no user element that has no values can be added.

The check for count>1024 is not needed because the count is checked
later for the individual control types.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>