usb: gadget: goku_udc: Fix error path

This is based on an initial patch by Rahul Ruikar.

The goku_remove() function can be called before device_register() so it
can call device_unregister() improperly.  Also if the call to
device_register() fails we need to call put_device().

As I was changing the error handling in goku_probe(), I noticed that
the label was "done" but actually if the function succeeds we return
earlier.  I renamed the error path to "err" instead of "done."

Reported-by: Rahul Ruikar <rahul.ruikar@gmail.com>
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>