exynos4-is: remove some unused vars

Gcc 6.1 warns about some unused vars and functions. Remove them:

drivers/media/platform/exynos4-is/mipi-csis.c:665:46: warning: 's5pcsis_sd_internal_ops' defined but not used [-Wunused-const-variable=]
 static const struct v4l2_subdev_internal_ops s5pcsis_sd_internal_ops = {
                                              ^~~~~~~~~~~~~~~~~~~~~~~

drivers/media/platform/exynos4-is/mipi-csis.c:652:12: warning: 's5pcsis_open' defined but not used [-Wunused-function]
 static int s5pcsis_open(struct v4l2_subdev *sd, struct v4l2_subdev_fh *fh)
            ^~~~~~~~~~~~

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>