ALSA: fix selector unit bug affecting some USB speakerphones

ALSA: fix selector unit bug affecting some USB speakerphones

patch 38977e96cb32e658716e11a05ec7f1fc4618e0f3 in mainline.

[ALSA] fix selector unit bug affecting some USB speakerphones

Following the suggestion in this thread:
https://bugs.launchpad.net/ubuntu/+source/alsa-lib/+bug/26683
the correct upper bound on desc[0] is 5 + num_ins not 6 + num_ins,
because the index used later is 5+i, not 6+i.
This change makes my Vosky Chatterbox speakerphone work.
Apparently it also helps with the Minivox MV100.

Signed-off-by: Russ Cox <rsc@swtch.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>