ARM: imx6sl: Add missing pll4_audio_div to the clock tree

There's a dividor for pll4_audio clock missing in clock tree, thus add it.

Signed-off-by: Nicolin Chen <Guangyu.Chen@freescale.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

include/dt-bindings/clock/imx6sl-clock.h

@@ -143,6 +143,7 @@
 #define IMX6SL_CLK_USDHC2		130
 #define IMX6SL_CLK_USDHC3		131
 #define IMX6SL_CLK_USDHC4		132
-#define IMX6SL_CLK_END			133
+#define IMX6SL_CLK_PLL4_AUDIO_DIV	133
+#define IMX6SL_CLK_END			134
 
 #endif /* __DT_BINDINGS_CLOCK_IMX6SL_H */