Under a UEFI environment, pci_bios_get_irq_routing() returns 0 and also sets *nneededp to 0; this causes a small leak in pci_get_irq_routing_table().

kmem_alloc_512 leak: 1 buffer, 512 bytes
            ADDR          BUFADDR        TIMESTAMP           THREAD
                            CACHE          LASTLOG         CONTENTS
ffffff0708721018 ffffff0708706b80                0 fffffffffbc53040
                 ffffff06e1038648 ffffff06e6017a00                0
                 kmem_cache_alloc_debug+0x2fc
                 kmem_cache_alloc+0x25b
                 kmem_zalloc+0x47
                 pci_get_irq_routing_table+0x27
                 startup_pci_bios+9
                 startup+0x4a
                 main+0x96
                 _locore_start+0x90