base: Initialize some variables in the wide multiply helpers.
base: Initialize some variables in the wide multiply helpers.

Not initializing them seems to upset older versions of g++.

Change-Id: Ib3de0460463f2fe514175484c49e1df68dacb4d3
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/45819
Reviewed-by: Daniel Carvalho <91779fc734d358d9575ec4910de29bfcbcaf1b22@yahoo.com.br>
Reviewed-by: Matt Sinclair <d2406197fb1bedd1e23c70c50c510ff0e9ab0f5b@gmail.com>
Maintainer: Gabe Black <d3e8afea784ab4a50a2dbf9149d2eaa8478e1cbc@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5