PCI/AER: Unexport pci_enable_pcie_error_reporting()

pci_enable_pcie_error_reporting() is used only inside aer.c.  Stop exposing
it outside the file.

Link: https://lore.kernel.org/r/20230710232136.233034-3-helgaas@kernel.org


Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>