b43: add Kconfig option for compiling SSB driver

It is always "y" for now, b43 will not compile without CONFIG_SSB yet.
This is just a first step of dropping SSB dependency.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/b43/bus.c b/drivers/net/wireless/b43/bus.c
index 8a10b82..4200713 100644
--- a/drivers/net/wireless/b43/bus.c
+++ b/drivers/net/wireless/b43/bus.c
@@ -25,7 +25,7 @@
 
 
 /* SSB */
-
+#ifdef CONFIG_B43_SSB
 static inline int b43_bus_ssb_bus_may_powerdown(struct b43_bus_dev *dev)
 {
 	return ssb_bus_may_powerdown(dev->sdev->bus);
@@ -124,3 +124,4 @@
 
 	return dev;
 }
+#endif /* CONFIG_B43_SSB */