This is a more detailed guide 
First of all you should type:
. /lib/functions/system.sh
find /proc/device-tree/ -name "*mac-address*"
it will output something like this:
/proc/device-tree/ahb/eth@19000000
/proc/device-tree/ahb/eth@1a000000
/proc/device-tree/ahb/wmac@18100000
Now, for every path, you have to type:
get_mac_binary "PATH" 0
for example, if the path is: /proc/device-tree/ahb/eth@19000000 you have to type:
get_mac_binary "/proc/device-tree/ahb/eth@19000000/mac-address" 0
and so on.
Let me know! 