dcache: Fix bug in store hit after dcbz case

dcache: Fix bug in store hit after dcbz case

This fixes a bug where a store that hits in the dcache immediately
following a dcbz has its write to the cache RAM suppressed (but not
its write to memory).  If a load to the same location comes along
before the cache line gets replaced, the load will return incorrect
data.

Fixes: 4db1676ef8b3 ("dcache: Don't assert on dcbz cache hit")
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>