lantiq: xrx200: handle EPROBE_DEFER for MAC address

lantiq: xrx200: handle EPROBE_DEFER for MAC address

The xrx200 ethernet driver falls back to a random MAC address on any
error from of_get_ethdev_address(), including -EPROBE_DEFER. When the
MAC address comes from an nvmem layout driver (such as u-boot-env on
NAND), the nvmem cell may not be available yet at first probe attempt.

Fix this by propagating EPROBE_DEFER so the driver probe is deferred
until the nvmem cell becomes available.

Tested on Zyxel P-2812HNU-F1 (NAND, u-boot-env nvmem layout).

Signed-off-by: Burak Aydos <byhexadecimal@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/21861
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>