hw/ppc: rename functions in comments

Commit bcb5ce08 ("spapr: Rename machine init functions for clarity")
renamed ppc_spapr_reset to spapr_machine_reset and ppc_spapr_init
to spapr_machine_init. Let's also rename the references in
comments.

Signed-off-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>