man: fix a typo in MPI_Ibarrier C prototype

Thanks Harald Servat for reporting this

(cherry picked from commit open-mpi/ompi@97b9d12)

Author: ggouaillardet

ompi/mpi/man/man3/MPI_Barrier.3in

@@ -14,7 +14,7 @@
 #include <mpi.h>
 int MPI_Barrier(MPI_Comm \fIcomm\fP)
 
-int MPI_Ibarrier(MPI_Comm \fIcomm\fP, MPI_Request \fIrequest\fP)
+int MPI_Ibarrier(MPI_Comm \fIcomm\fP, MPI_Request \fI*request\fP)
 
 .fi
 .SH Fortran Syntax