pc: replace pm object initialization with one-liner in acpi_get_pm_info()

pc: replace pm object initialization with one-liner in acpi_get_pm_info()

next patch will need it before it gets to piix4/lpc branches
that initializes 'obj' now.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Tested-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>