Remove redundant use of always for a_dmhaltaddr_stable

For reasons unknown, the addition of a_dmhaltaddr_stable cause Metrics DSIM simulations of some (but not all) testcases to drastically slow down. For example, "make test TEST=interrupt_test" goes from ~8.5 minutes to more than 87 minutes. Oddly, the simulation runs correctly, it just takes a very long time. I have raised a support issue with Metrics.

The code that causes this issue is changed in this PR. A redundant whitespace (2'b 00) is also fixed, but that is of no consequence to either xrun or dsim. Please have a look and satisfy yourself that I have not broken anything.

Signed-off-by: Mike Thompson mike@openhwgroup.org