ACPI: x86: s2idle: Catch multiple ACPI_TYPE_PACKAGE objects

If a badly constructed firmware includes multiple `ACPI_TYPE_PACKAGE`
objects while evaluating the AMD LPS0 _DSM, there will be a memory
leak.  Explicitly guard against this.

Suggested-by: Bjorn Helgaas <helgaas@kernel.org>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>