inject: fix mac address insertion

during previous re-factoring, i sorted variable initialisations.

that was all well and good, but prior to that, i initialised
the new_mac string to empty at first, and then to
the "xx" letters; the latter made the first initialisation
redundant, but in the re-factoring, I put the blanking of
the string afterward.

this disabled mac address insertion, because the way the script
works is precisely to avoid mac address insertion when the mac
string is empty. this is used when running the "nuke" command.

silly me.

yes, i'm very silly. very very silly. so silly.

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/inject.sh

@@ -40,7 +40,6 @@ inject()
 	archive="$1";
 	new_mac="xx:xx:xx:xx:xx:xx"
 
-	new_mac=""
 	nuke=""
 	xchanged=""