virt: haven: rm_core: Re-use alloc'd message when sending requests

No need to allocate a message queue buffer for each message queue
fragment, re-use the same one.

Change-Id: I5743a704ec08732a2e405724ba795d2d8cea90e3
Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
Signed-off-by: Srinivasarao Pathipati <quic_c_spathi@quicinc.com>