MT#63853 isolinux: fix file path for chain.c32 module

The file path was adjusted in grml-live upstream
commit 303888ac617cee40f82b61190071d92b4f82de96

Otherwise the "Boot from ... boot device" entries fail to run due to:

  Failed to load COM32 file /boot/addons/chain.c32

As reported by Mike Jackson on spce-user ML.

Change-Id: Id06d4c53f4fab043e093bba6e2e95f1936610271

isolinux.cfg

@@ -188,7 +188,7 @@ label ipxe
 
 label hd1
   menu label ^Boot from primary local boot device
-  kernel /boot/addons/chain.c32
+  kernel /boot/isolinux/chain.c32
   append hd0 0
   text help
                                      Boot from 1st local boot device -
@@ -197,7 +197,7 @@ label hd1
 
 label hd2
   menu label ^Boot from secondary local boot device
-  kernel /boot/addons/chain.c32
+  kernel /boot/isolinux/chain.c32
   append hd1 0
   text help
                                      Boot from 2nd local boot device -
@@ -206,7 +206,7 @@ label hd2
 
 label hd3
   menu label ^Boot from third local boot device
-  kernel /boot/addons/chain.c32
+  kernel /boot/isolinux/chain.c32
   append hd2 0
   text help
                                      Boot from 3rd local boot device -
@@ -215,7 +215,7 @@ label hd3
 
 label hd4
   menu label ^Boot from fourth local boot device
-  kernel /boot/addons/chain.c32
+  kernel /boot/isolinux/chain.c32
   append hd3 0
   text help
                                      Boot from 4th local boot device -