drm: armada: make of_device_ids const.

of_device_ids are not supposed to change at runtime. All functions
working with of_device_ids provided by <linux/of.h> work with const
of_device_ids. So mark the non-const structs as const.

File size before:
   text	   data	    bss	    dec	    hex	filename
   8836	    744	      0	   9580	   256c	drivers/gpu/drm/armada/armada_crtc.o

File size after constify armada_lcd_of_match:
   text	   data	    bss	    dec	    hex	filename
   9220	    328	      0	   9548	   254c	drivers/gpu/drm/armada/armada_crtc.o
Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/ff9a9a908cf347775ab62cfadfde986de72dcf13.1497935382.git.arvind.yadav.cs@gmail.com

drivers/gpu/drm/armada/armada_crtc.c

@@ -1364,7 +1364,7 @@ static int armada_lcd_remove(struct platform_device *pdev)
 	return 0;
 }
 
-static struct of_device_id armada_lcd_of_match[] = {
+static const struct of_device_id armada_lcd_of_match[] = {
 	{
 		.compatible	= "marvell,dove-lcd",
 		.data		= &armada510_ops,