ARM i.MX: remove duplicated include from clk-imx21.c

From: Wei Yongjun <yongjun_wei@trendmicro.com.cn>

Remove duplicated include.
Signed-off-by: NWei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: NSascha Hauer <s.hauer@pengutronix.de>

arch/arm/mach-imx/clk-imx21.c

@@ -23,7 +23,6 @@
 #include <linux/clk-provider.h>
 #include <linux/io.h>
 #include <linux/module.h>
-#include <linux/clkdev.h>
 #include <linux/err.h>
 
 #include <mach/hardware.h>