MIPS: ralink: add missing clk_set_rate() to clk.c

This function was missing causing make allmod to fail.
Signed-off-by: NJohn Crispin <blogic@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/8005/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/ralink/clk.c

@@ -56,6 +56,12 @@ unsigned long clk_get_rate(struct clk *clk)
 }
 EXPORT_SYMBOL_GPL(clk_get_rate);
 
+int clk_set_rate(struct clk *clk, unsigned long rate)
+{
+	return -1;
+}
+EXPORT_SYMBOL_GPL(clk_set_rate);
+
 void __init plat_time_init(void)
 {
 	struct clk *clk;