of_net: remove nvmem-mac-address property

In commit d01f449c ("of_net: add NVMEM support to
of_get_mac_address") I've added `nvmem-mac-address` property which was
wrong idea as I've allocated the property with devm_kzalloc and then
added it to DT, so then 2 entities would be refcounting the allocation.
So if the driver unbinds, the buffer is freed, but DT code would be
still referencing that memory.

I'm removing this property completely instead of fixing it, as it's not
needed to have it.

Fixes: d01f449c

 ("of_net: add NVMEM support to of_get_mac_address")
Suggested-by: Rob Herring <robh@kernel.org>
Signed-off-by: Petr Štetiar <ynezz@true.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>