PCI/PM: Simplify pci_set_power_state()

PCI/PM: Simplify pci_set_power_state()

Check for the PCI_DEV_FLAGS_NO_D3 quirk early, before calling
__pci_start_power_transition().  This way all the cases where we don't need
to do anything at all are checked up front.

This doesn't fix anything because if the caller requested D3hot or D3cold,
__pci_start_power_transition() is a no-op.  But calling it is pointless and
makes the code harder to analyze.

Link: https://lore.kernel.org/r/20191101204558.210235-4-helgaas@kernel.org
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>