DTU: always allow write access to receive buffers.
DTU: always allow write access to receive buffers.

Change-Id: I

TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,TUD-OS/gem5-dtu,TUD-OS/gem5-dtu