drm: sti: sti_hqvdp: 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
  15845	    640	      0	  16485	   4065	drivers/gpu/drm/sti/sti_hqvdp.o

File size after constify hqvdp_of_match:
   text	   data	    bss	    dec	    hex	filename
  16229	    224	      0	  16453	   4045	drivers/gpu/drm/sti/sti_hqvdp.o
Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Link: http://patchwork.freedesktop.org/patch/msgid/0a6ae44cf7d0fb54380809ae0e52234dbd3f367a.1497934979.git.arvind.yadav.cs@gmail.com

drivers/gpu/drm/sti/sti_hqvdp.c

@@ -1395,7 +1395,7 @@ static int sti_hqvdp_remove(struct platform_device *pdev)
 	return 0;
 }
 
-static struct of_device_id hqvdp_of_match[] = {
+static const struct of_device_id hqvdp_of_match[] = {
 	{ .compatible = "st,stih407-hqvdp", },
 	{ /* end node */ }
 };