[MIPS] IP27: Delete useless declaration of allocate_irqno().

Signed-off-by: Ralf Baechle <[e-mail]>

arch/mips/pci/pci-ip27.c

···
 #include <asm/sn/intr.h>
 #include <asm/sn/sn0/hub.h>
 
-extern unsigned int allocate_irqno(void);
-
 /*
  * Max #PCI busses we can handle; ie, max #PCI bridges.
  */