MIPS: lantiq: add clk_round_rate()

This adds a basic implementation of clk_round_rate()
The clk_round_rate() function is called by multiple drivers and
subsystems now and the lantiq clk driver is supposed to export this,
but doesn't do so, this causes linking problems like this one:
ERROR: "clk_round_rate" [drivers/media/v4l2-core/videodev.ko] undefined!
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Acked-by: John Crispin <blogic@openwrt.org>
Cc: <stable@vger.kernel.org> # 4.1+
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11358/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/lantiq/clk.c

@@ -99,6 +99,23 @@ int clk_set_rate(struct clk *clk, unsigned long rate)
 }
 EXPORT_SYMBOL(clk_set_rate);
 
+long clk_round_rate(struct clk *clk, unsigned long rate)
+{
+	if (unlikely(!clk_good(clk)))
+		return 0;
+	if (clk->rates && *clk->rates) {
+		unsigned long *r = clk->rates;
+
+		while (*r && (*r != rate))
+			r++;
+		if (!*r) {
+			return clk->rate;
+		}
+	}
+	return rate;
+}
+EXPORT_SYMBOL(clk_round_rate);
+
 int clk_enable(struct clk *clk)
 {
 	if (unlikely(!clk_good(clk)))