Fix an off-by-one error in the dma tag.  This was causing the VM system to freak out occasionally.
Fix an off-by-one error in the dma tag.  This was causing the VM system to
freak out occasionally.

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