ARM: mach-imx: clk-gate2: Include "clk.h"

Fix the following sparse warning:

arch/arm/mach-imx/clk-gate2.c:86:12: warning: symbol 'clk_register_gate2' was not declared. Should it be static?
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: NShawn Guo <shawn.guo@linaro.org>

arch/arm/mach-imx/clk-gate2.c

@@ -15,6 +15,7 @@
 #include <linux/io.h>
 #include <linux/err.h>
 #include <linux/string.h>
+#include "clk.h"
 
 /**
  * DOC: basic gatable clock which can gate and ungate it's ouput