PCI / PM: Fix D3/D3cold/D4 messages printed by acpi_pci_set_power_state()

If a PCI device is put into D3_cold by acpi_bus_set_power(),
the message printed by acpi_pci_set_power_state() says that its
power state has been changed to D4, which doesn't make sense.
In turn, if the device is put into D3_hot, the message simply
says "D3" without specifying the variant of the D3 state.

Fix this by using the pci_power_name() macro for printing the state
name instead of building it from the numeric value corresponding to
the given state directly.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>