Make legacy ATA to not call device_add_child() with unit number but without driver name. This fixed legacy ATA breakage by r235978.
Make legacy ATA to not call device_add_child() with unit number but
without driver name. This fixed legacy ATA breakage by r235978.

MFC after:	1 week

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase