OSHMEM: spml ikrit: complete puts b4 memheap destruction

Force completion of all puts before deregestering memheap/bss memory

Fixes a possible race condition where put request completion callback
is called when request context is already cleared.

cherry picked from commit open-mpi/ompi@5af4d02bd3b601a18f6fb03b1837fceb6534261e

@miked-mellanox @jladd-mlnx