ARM: dove: Add clock-names to CuBox Si5351 clk generator

Si5351 clock generator on CuBox uses XTAL as clock reference, name the
clock phandle accordingly.
Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>

arch/arm/boot/dts/dove-cubox.dts

@@ -87,6 +87,7 @@ si5351: clock-generator {
 
 		/* connect xtal input to 25MHz reference */
 		clocks = <&ref25>;
+		clock-names = "xtal";
 
 		/* connect xtal input as source of pll0 and pll1 */
 		silabs,pll-source = <0 0>, <1 0>;