dcache: Don't assert on dcbz cache hit

dcache: Don't assert on dcbz cache hit

We can hit the assert for req_op = OP_STORE_HIT and reloading in the
case of dcbz, since it looks like a store.  Therefore we need to
exclude that case from the assert.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>