rtas_st_buffer_direct() is a not particularly useful wrapper around
cpu_physical_memory_write(). All the callers are in
rtas_ibm_configure_connector, where it's better handled by local helper.
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.ru>