ssb: fix NULL ptr deref when pcihost_wrapper is used

Ethernet driver b44 does register ssb by it's pcihost_wrapper
and doesn't set ssb_chipcommon. A check on this value
introduced with commit d53cdbb94a
and ea2db495f9 triggers:

BUG: unable to handle kernel NULL pointer dereference at 00000010
IP: [<c1266c36>] ssb_is_sprom_available+0x16/0x30

Signed-off-by: Christoph Fritz <chf.fritz@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/ssb/pci.c

@@ -625,9 +625,12 @@ static int ssb_pci_sprom_get(struct ssb_bus *bus,
 		ssb_printk(KERN_ERR PFX "No SPROM available!\n");
 		return -ENODEV;
 	}
-
-	bus->sprom_offset = (bus->chipco.dev->id.revision < 31) ?
-		SSB_SPROM_BASE1 : SSB_SPROM_BASE31;
+	if (bus->chipco.dev) {	/* can be unavailible! */
+		bus->sprom_offset = (bus->chipco.dev->id.revision < 31) ?
+			SSB_SPROM_BASE1 : SSB_SPROM_BASE31;
+	} else {
+		bus->sprom_offset = SSB_SPROM_BASE1;
+	}
 
 	buf = kcalloc(SSB_SPROMSIZE_WORDS_R123, sizeof(u16), GFP_KERNEL);
 	if (!buf)

drivers/ssb/sprom.c

@@ -185,6 +185,7 @@ bool ssb_is_sprom_available(struct ssb_bus *bus)
 	/* this routine differs from specs as we do not access SPROM directly
 	   on PCMCIA */
 	if (bus->bustype == SSB_BUSTYPE_PCI &&
+	    bus->chipco.dev &&	/* can be unavailible! */
 	    bus->chipco.dev->id.revision >= 31)
 		return bus->chipco.capabilities & SSB_CHIPCO_CAP_SPROM;