usb: gadget: uac2: add some error recovery in afunc_bind()

In case something goes wrong here, don't leak memory / endpoints.

Acked-by: Jassi Brar <jassisinghbrar@gmail.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>