rebuild-kc: use --bootefi with bless

I'm not 100% sure this is the correct way to fix this, but it likely is,
and I think it's better than leaving this unfixed any longer.

(Once Big Sur beta 11 comes out, I'll see if this method also works
with patch-kexts.sh, and I'll change it if so.)

Author: barrykn

payloads/rebuild-kc.sh

@@ -133,7 +133,7 @@ fi
 if [ "$VOLUME" != "/" ]
 then
     echo 'Creating new root snapshot.'
-    bless --folder "$VOLUME"/System/Library/CoreServices --create-snapshot
+    bless --folder "$VOLUME"/System/Library/CoreServices --create-snapshot --bootefi
     if [ $? -ne 0 ]
     then
         echo