ALSA: echoaudio: read past end of array

We need to cap "ucontrol->id.index / num_busses_in(chip)" so the we
don't read beyond the end of the array.

I also adding a check on "in" and changing the type in
snd_echo_mixer_put() from short to unsigned int. Those changes are done
for symmetry and are cosmetic.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>