mem-cache: Fix bug in handleAtomicReqMiss

mem-cache: Fix bug in handleAtomicReqMiss

"4976ff5 mem-cache: Refactor the recvAtomic function" introduced a bug
where if an atomic request that fills in using the tempBlock it will
not evict it when it finishes handling the request as it should. This
triggers an assertion. This change fixes this bug.

Change-Id: I73c808a7e15237eddb36b5448ef6728f7bcf7fd9
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/12644
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>