Fix two bugs reported by Don Koch <aardvark@poirot.krl.com>(NetBSD PR#216{8,9})

Fix two bugs reported by Don Koch <aardvark@poirot.krl.com>(NetBSD PR#216{8,9})
 [1] check return value from malloc() for NULL before trying to bzero it.
 [2] use "=" rather than "|=" when writing to CSR (otherwise you may
        ACK something you don't mean to!).