PCI/PM: Fold __pci_start_power_transition() into its caller

PCI/PM: Fold __pci_start_power_transition() into its caller

Because pci_power_up() has become the only caller of
__pci_start_power_transition(), there is no need for the latter to
be a separate function any more, so fold it into the former, drop a
redundant check and reduce the number of lines of code somewhat.

Code rearrangement, no intentional functional impact.

Link: https://lore.kernel.org/r/3458080.lsoDbfkST9@kreacher
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>