MIPS: remove alloc_pci_controller prototype

Commit 610019ba ("[MIPS] Remove unused
function alloc_pci_controller.") removed the function, but left the
prototype in the header file.

Remove it as well so people don't get tempted to use it and wonder why
it doesn't work.
Signed-off-by: Jonas Gorski <jogo@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/5473/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/pci.h

@@ -52,7 +52,6 @@ struct pci_controller {
 /*
  * Used by boards to register their PCI busses before the actual scanning.
  */
-extern struct pci_controller * alloc_pci_controller(void);
 extern void register_pci_controller(struct pci_controller *hose);
 
 /*