ARM: pxa: add clk_set_rate()

Since there're mulitple clock rates in some device controllers, enable
clk_set_rate() for this usage.

Signed-off-by: Haojian Zhuang <haojian.zhuang@marvell.com>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>
diff --git a/arch/arm/mach-pxa/clock.h b/arch/arm/mach-pxa/clock.h
index 1f2fb9c..3a258b1 100644
--- a/arch/arm/mach-pxa/clock.h
+++ b/arch/arm/mach-pxa/clock.h
@@ -5,6 +5,7 @@
 	void			(*enable)(struct clk *);
 	void			(*disable)(struct clk *);
 	unsigned long		(*getrate)(struct clk *);
+	int			(*setrate)(struct clk *, unsigned long);
 };
 
 struct clk {