Updating backing build

Change-Id: I862d52f40b5459d73c0dafe6c84611a3d8c7726f
Reviewed-on: http://ralgit01.raleigh.ibm.com/gerrit1/62873
Tested-by: Jenkins Server <pfd-jenkins+hostboot@us.ibm.com>
Reviewed-by: Sachin Gupta <sgupta2m@in.ibm.com>

customrc

@@ -33,6 +33,6 @@ export SANDBOXNAME=test_sb
 #export WORKSPACE=<set it to your root ppe directory. This is required if you
 #                  to use build script locally>
 export MACHINE=NIMBUS
-export BACKING_BUILD=/esw/fips920/Builds/b0620a_1825.920/
+export BACKING_BUILD=/esw/fips921/Builds/b0718a_1829.921/
 export SIMICSOPTIONS="-nre"