ramips: add missing clk_round_rate function to fix buildbot errors

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

SVN-Revision: 48024

target/linux/ramips/patches-4.3/0064-add_clk_round_rate.patch

@@ -0,0 +1,15 @@
+--- a/arch/mips/ralink/clk.c
++++ b/arch/mips/ralink/clk.c
+@@ -62,6 +62,12 @@ int clk_set_rate(struct clk *clk, unsign
+ }
+ EXPORT_SYMBOL_GPL(clk_set_rate);
+ 
++long clk_round_rate(struct clk *clk, unsigned long rate)
++{
++	return -1;
++}
++EXPORT_SYMBOL_GPL(clk_round_rate);
++
+ void __init plat_time_init(void)
+ {
+ 	struct clk *clk;