ofi mtl: fix problem with mrecv

the ofi mtl mrecv was not properly setting the message in/out
arg to MPI_MRECV to MPI_MESSAGE_NULL.

Signed-off-by: Howard Pritchard <hppritcha@gmail.com>

ompi/mca/mtl/ofi/mtl_ofi.h

@@ -950,6 +950,8 @@ ompi_mtl_ofi_imrecv(struct mca_mtl_base_module_t *mtl,
         return ompi_mtl_ofi_get_error(ret);
     }
 
+    *message = MPI_MESSAGE_NULL;
+
     return OMPI_SUCCESS;
 }