The remaining functions added by commit
a8ea8bdd9df92a0e5db5b43900abb7a288b8a53e did not check for memory
allocation errors. Add the checks and change the API to allow errors
to be returned.
Fixes: a8ea8bdd9df9 ("lib/mpi: Extend the MPI library")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>