PCI/ASPM: Move pci_clear_and_set_dword() earlier

Move pci_clear_and_set_dword() earlier in file to prepare for future patch.
No functional change intended.

Link: https://lore.kernel.org/r/20201015193039.12585-2-helgaas@kernel.org


Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>