net: usb: asix88179_178a: set permanent address once only

The permanent address of asix88179_178a devices is read at probe time
and should not be overwritten later. Otherwise it may be overwritten
unintentionally with a configured address.

Signed-off-by: Alexander Kurz <akurz@blala.de>
Signed-off-by: David S. Miller <davem@davemloft.net>