blackfin: bf60x: make clock changeable in kernel menuconfig

Add clock changeable support in kernel menuconfig for bf60x.

Signed-off-by: Bob Liu <lliubbo@gmail.com>
diff --git a/arch/blackfin/mach-bf609/clock.c b/arch/blackfin/mach-bf609/clock.c
index b50412c..7f8f529 100644
--- a/arch/blackfin/mach-bf609/clock.c
+++ b/arch/blackfin/mach-bf609/clock.c
@@ -351,7 +351,7 @@
 	.rate       = 500000000,
 	.mask       = CGU0_DIV_DSEL_MASK,
 	.shift       = CGU0_DIV_DSEL_SHIFT,
-	.parent     = &pll_clk,
+	.parent     = &sys_clkin,
 	.ops	    = &sys_clk_ops,
 };