Revert "ath79: elecom,wab: use nvmem"

Revert "ath79: elecom,wab: use nvmem"

This reverts commit 70e41d0205d95386881fa1cdf6ee00f6cca1b3f6.

"ethaddr" is stored into the "u-boot-env" (stock: "Config") partition
and it's quoted with double-quotations, but that format is not supported
by the current NVMEM u-boot-env driver (and mac_pton() function) and the
MAC address won't be parsed to byte array.
This causes random MAC addresses on the adapters, so revert the above
commit.

Signed-off-by: INAGAKI Hiroshi <musashino.open@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/17116
Signed-off-by: Robert Marko <robimarko@gmail.com>