fakelb: rename fakelb_dev_priv to fakelb_phy

This patch renames fakelb_dev_priv to fakelb_phy. We don't faking
devices here, we fake wpan phys. This avoids also confusing with the
variable priv, which is used several times in this driver to represent
this structure.

Signed-off-by: Alexander Aring <alex.aring@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>