PCI / PM: Clean up outdated comments in pci_target_state()

Two comments in pci_target_state() are outdated, as the function
doesn't set the target power state for the device any more, only
finds one for it, so fix them accordingly.

Reported-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>