alsa-mixer: Fix Analog Input showing up on USB Headset

alsa-mixer: Fix Analog Input showing up on USB Headset

In some cases, "Analog Input" could show up as well as
"Headset Mic" (or "Headphone Mic"), because I forgot to add the
relevant "required-absent" lines when I added the headset mic path.

As a result, both "Analog Input" and "Headset Mic" showed up on the
Logitech USB 530 Headset.

Reported-by: Steve Magoun <steve.magoun@canonical.com>
Signed-off-by: David Henningsson <david.henningsson@canonical.com>