PCI/AER: Remove duplicate pcie_port_bus_type declaration

pcie_port_bus_type is already declared in portdrv.h, so remove the
unnecessary duplicate declaration in aerdrv.h.  No functional change
intended.
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Reviewed-by: NKeith Busch <keith.busch@intel.com>

drivers/pci/pcie/aer/aerdrv.h

@@ -76,7 +76,6 @@ struct aer_rpc {
 					 */
 };
 
-extern struct bus_type pcie_port_bus_type;
 irqreturn_t aer_irq(int irq, void *context);
 
 #ifdef CONFIG_ACPI_APEI