client-architecture-support: fix redundant stack drop

This removes dropping allocated memory buffer off the stack in the case
when no change to the tree was generated by QEMU.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
client-architecture-support: fix wrong version read

This fixed size of reading the version (which is actually 32bit), this
removes confusing "cas not implemented" message from the guest.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>