usb: fix usb_qdev_init() error handling again

Commit f462141f introduced clean up code
when usb_qdev_init() fails.  Unfortunately it calls .handle_destroy()
when .init() was never invoked or failed.  This can lead to crashes when
.handle_destroy() tries to clean up things that were never initialized.

This patch is careful to undo only those steps that completed along the
usb_qdev_init() code path.  It's not as pretty as the unified error
handling in f462141f but it's necessary.

Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>