ARM: dts: omap5-board-common: Add phandle for mclk clock for twl6040

The xref_xtal clock is used by twl6040 as mclk. It is needed for the HPPLL
internally.
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/boot/dts/omap5-board-common.dtsi

@@ -659,8 +659,8 @@ twl6040: twl@4b {
 		v2v1-supply = <&smps9_reg>;
 		enable-active-high;
 
-		clocks = <&clk32kgaudio>;
-		clock-names = "clk32k";
+		clocks = <&clk32kgaudio>, <&fref_xtal_ck>;
+		clock-names = "clk32k", "mclk";
 	};
 };