PCI: dwc: Make dw_pcie_ptm_ops static

PCI: dwc: Make dw_pcie_ptm_ops static

dw_pcie_ptm_ops is not used outside of this file, so make it static. This
also fixes the sparse warning:

  drivers/pci/controller/dwc/pcie-designware-debugfs.c:868:27: warning: symbol 'dw_pcie_ptm_ops' was not declared. Should it be static?

Fixes: 852a1fdd34a8 ("PCI: dwc: Add debugfs support for PTM context")
Reported-by: Bjorn Helgaas <helgaas@kernel.org>
Closes: https://lore.kernel.org/linux-pci/20250617231210.GA1172093@bhelgaas
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://patch.msgid.link/20250701120856.15839-1-mani@kernel.org