ARM: imx: Include linux/err.h

The IS_ERR() macro is defined in the linux/err.h header file, so include
it explicitly.
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>

arch/arm/mach-imx/cpu.c

-
+#include <linux/err.h>
 #include <linux/module.h>
 #include <linux/io.h>
 #include <linux/of.h>