Blackfin: fix unused clk var warning

This is only used on BF60x code (so this patch should get squashed into
the original one that added it).

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Bob Liu <lliubbo@gmail.com>
diff --git a/arch/blackfin/kernel/setup.c b/arch/blackfin/kernel/setup.c
index c113cfa..ed04154 100644
--- a/arch/blackfin/kernel/setup.c
+++ b/arch/blackfin/kernel/setup.c
@@ -892,7 +892,9 @@
 {
 	u32 mmr;
 	unsigned long sclk, cclk;
+#ifdef CONFIG_BF60x
 	struct clk *clk;
+#endif
 
 	native_machine_early_platform_add_devices();