usb: gadget: f_uac2: Fix sound card registration failure

Sound card registration fails when adb is rerun as root.
The cause is the limitation in kernel/ALSA in proper
cleaning up of the  the parent of sound card when the sound
card is removed. Fix this by pointing to a parent that
will not be removed during sound card free.

Change-Id: Id9354be1c2dc459fbd0a88be4ff3f167dff8f4d9
Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>