Fix a DCache read completion bug with multi-register loads.
Fix a DCache read completion bug with multi-register loads.

This bug was introduced in Match 2013
(7eb5aab3652154d119bc42c9e690c6e6aa654ad6)
when asynchronous writebacks were implemented.

Bitblade-org/mgsim,Bitblade-org/mgsim,Bitblade-org/mgsim,Bitblade-org/mgsim