PCI/PM: Rearrange pci_update_current_state()

Save one config space access in pci_update_current_state() by testing the
retrieved PCI_PM_CTRL register value against PCI_POSSIBLE_ERROR() instead
of invoking pci_device_is_present() separately.

While at it, drop a pair of unnecessary parens.

No expected functional impact.

Link: https://lore.kernel.org/r/1917095.PYKUYFuaPT@kreacher


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