Warnings from AsyncCommPeer.C

[MrBurmark]

With hip clang we get a warning from two lines (849, 850) of AsyncCommPeer.C here https://github.com/LLNL/SAMRAI/blob/master/source/SAMRAI/tbox/AsyncCommPeer.C#L849.

The warning: warning: cast to 'void *' from smaller integer type 'SAMRAI_MPI::Request' (aka 'int') [-Wint-to-void-pointer-cast]