Bluetooth: btusb: fix PM leak in error case of setup

If setup() fails a reference for runtime PM has already
been taken. Proper use of the error handling in btusb_open()is needed.
You cannot just return.

Fixes: ace31982

 ("Bluetooth: btusb: Add setup callback for chip init on USB")
Signed-off-by: Oliver Neukum <oneukum@suse.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>