ARM: mvebu: kirkwood: remove error message when retrieving mac address

Kirkwood has always had the ability to retrieve the local-mac-address
from the hardware (usually this was configured by the bootloader). This
is particularly useful when dealing with a legacy non-DT aware
bootloader.

The "error" message just indicated that the board used an old bootloader
and in many cases users can't do anything about this. The message
probably should have been pr_info() to inform the user that the kernel
has been helpful but rather than than let's remove it entirely to make
the kernel less noisy.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>