staging: rtl8723au: Do not reset wdev->iftype in netdev_close()

wdev->ifdev should be set by .change_virtual_intf(). This solves the
problem of WARN() messages on module unload.

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>