mem-cache: Remove mumBlock redundant initialiation from FALRU

Change-Id: Id3afec0a62446d6d0f44ccb655032343037637e0
Reviewed-by: Curtis Dunham <curtis.dunham@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/8281
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>