bcma: use fallback sprom if sprom on card was not valid

Sometimes the PCIe card indicates that it has a sprom somewhere and we
are able to read the memory region, but it is empty and not valid. In
these cases we should try to use the fallback sprom as a last chance.

This is the case for the PCIe cards in my ASUS RT-N66U (BCM4706 + 2
times BCM4331) and I have heard of someone having the same problem with
an other PCIe card connected to an other Broadcom SoC.
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/bcma/sprom.c

@@ -595,8 +595,11 @@ int bcma_sprom_get(struct bcma_bus *bus)
 		bcma_chipco_bcm4331_ext_pa_lines_ctl(&bus->drv_cc, true);
 
 	err = bcma_sprom_valid(sprom);
-	if (err)
+	if (err) {
+		bcma_warn(bus, "invalid sprom read from the PCIe card, try to use fallback sprom\n");
+		err = bcma_fill_sprom_with_fallback(bus, &bus->sprom);
 		goto out;
+	}
 
 	bcma_sprom_extract_r8(bus, sprom);