mem-cache: Simplify writeback for the tempBlock in recvTimingResp

mem-cache: Simplify writeback for the tempBlock in recvTimingResp

When we use the tempBlock to fill-in, we have to write it back and
invalidate it at the end of current transaction. This patch simplifies
the writeback flow by treating it as a regular writeback.

Change-Id: I257be7bbff211e2832ad001a4e991daf67704485
Reviewed-on: https://gem5-review.googlesource.com/10421
Reviewed-by: Daniel Carvalho <odanrc@yahoo.com.br>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Nikos Nikoleris <nikos.nikoleris@arm.com>