usb: don't update devnum for wusb devices

For WUSB devices, usb_dev.devnum is a device index and not the real
device address (which is managed by wusbcore).  Therefore, only set
devnum once (in choose_address()) and never change it.

Signed-off-by: David Vrabel <david.vrabel@csr.com>
Cc: Inaky Perez-Gonzalez <inaky@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>