media: usb: go7007: s2250-board: fix leak in probe()

Call i2c_unregister_device(audio) on this error path.

Fixes: d3b2ccd9

 ("[media] s2250: convert to the control framework")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>