ACPI: tools: pfrut: Do not initialize ret in main()

The initialization is unnecessary, because ret is always assigned a new
value before reading it.

Signed-off-by: Shi junming <junming@nfschina.com>
[ rjw: Subject edits, new changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>