drm/exynos: exynos7_drm_decon: Consstify struct decon_data

static 'struct decon_data' is only read, so it can be const for code
safety.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

Author: krzk

drivers/gpu/drm/exynos/exynos7_drm_decon.c

@@ -43,13 +43,13 @@ struct decon_data {
 	unsigned int wincon_burstlen_shift;
 };
 
-static struct decon_data exynos7_decon_data = {
+static const struct decon_data exynos7_decon_data = {
 	.vidw_buf_start_base = 0x80,
 	.shadowcon_win_protect_shift = 10,
 	.wincon_burstlen_shift = 11,
 };
 
-static struct decon_data exynos7870_decon_data = {
+static const struct decon_data exynos7870_decon_data = {
 	.vidw_buf_start_base = 0x880,
 	.shadowcon_win_protect_shift = 8,
 	.wincon_burstlen_shift = 10,