SSB: hide empty sub menu

If the target system cannot support SSB, then don't show the menu option as
it'll simply be an empty submenu.
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/ssb/Kconfig

-menu "Sonics Silicon Backplane"
-
 config SSB_POSSIBLE
 	bool
 	depends on HAS_IOMEM && HAS_DMA
 	default y
 
+menu "Sonics Silicon Backplane"
+	depends on SSB_POSSIBLE
+
 config SSB
 	tristate "Sonics Silicon Backplane support"
 	depends on SSB_POSSIBLE