net: gianfar: fix NVMEM mac address

If nvmem loads after the ethernet driver, mac address assignments will
not take effect. of_get_ethdev_address returns EPROBE_DEFER in such a
case so we need to handle that to avoid eth_hw_addr_random.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20240910220913.14101-1-rosenp@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>