qcom-scm: Include <linux/err.h> header

Since commit e6f6d63e ("drm/msm: add headless gpu device for imx5")
the DRM_MSM symbol can be selected by SOC_IMX5 causing the following
error when building imx_v6_v7_defconfig:

In file included from ../drivers/gpu/drm/msm/adreno/a5xx_gpu.c:17:0:
../include/linux/qcom_scm.h: In function 'qcom_scm_set_cold_boot_addr':
../include/linux/qcom_scm.h:73:10: error: 'ENODEV' undeclared (first use in this function)
  return -ENODEV;

Include the <linux/err.h> header file to fix this problem.

Reported-by: kernelci.org bot <bot@kernelci.org>
Fixes: e6f6d63e ("drm/msm: add headless gpu device for imx5")
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Andy Gross <andy.gross@linaro.org>