Change MemReqPtr parameters to references.

Change MemReqPtr parameters to references.
This avoids incrementing and decrementing the MemReq
reference counters on every call and return.

arch/alpha/alpha_memory.cc:
arch/alpha/alpha_memory.hh:
cpu/exec_context.hh:
cpu/memtest/memtest.cc:
cpu/memtest/memtest.hh:
dev/alpha_console.cc:
dev/alpha_console.hh:
    Change MemReqPtr parameters to references.

--HG--
extra : convert_revision : 3ba18bdd9f996563988402576bfdd3430e1ab1e5