drm: Constify TV mode names

Make the mode names passed to drm_mode_create_tv_properties() const.

 drivers/gpu/drm/i2c/ch7006.ko:
-.rodata                       596
+.rodata                       664
-.data                        7064
+.data                        6992

 drivers/gpu/drm/nouveau/nouveau.ko:
-.rodata                      146808
+.rodata                      146904
-.data                        178624
+.data                        178528

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i2c/ch7006_priv.h b/drivers/gpu/drm/i2c/ch7006_priv.h
index ce57784..cef6ce7 100644
--- a/drivers/gpu/drm/i2c/ch7006_priv.h
+++ b/drivers/gpu/drm/i2c/ch7006_priv.h
@@ -106,7 +106,7 @@
 extern char *ch7006_tv_norm;
 extern int ch7006_scale;
 
-extern char *ch7006_tv_norm_names[];
+extern const char * const ch7006_tv_norm_names[];
 extern struct ch7006_tv_norm_info ch7006_tv_norms[];
 extern struct ch7006_mode ch7006_modes[];