drm: qxl: constify ttm_place structures.

ttm_place are not supposed to change at runtime. All functions
working with ttm_place provided by <drm/ttm/ttm_placement.h> work
with const ttm_place. So mark the non-const structs as const.

File size before:
   text	   data	    bss	    dec	    hex	filename
   3485	    184	    264	   3933	    f5d	drivers/gpu/drm/qxl/qxl_ttm.o

File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
   3501	    152	    264	   3917	    f4d	drivers/gpu/drm/qxl/qxl_ttm.o
Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Link: http://patchwork.freedesktop.org/patch/msgid/a4f21d3bd2497129f084b8055ecf27f0d3ff1bba.1499013516.git.arvind.yadav.cs@gmail.comSigned-off-by: Gerd Hoffmann <kraxel@redhat.com>

drivers/gpu/drm/qxl/qxl_ttm.c

@@ -187,7 +187,7 @@ static void qxl_evict_flags(struct ttm_buffer_object *bo,
 				struct ttm_placement *placement)
 {
 	struct qxl_bo *qbo;
-	static struct ttm_place placements = {
+	static const struct ttm_place placements = {
 		.fpfn = 0,
 		.lpfn = 0,
 		.flags = TTM_PL_MASK_CACHING | TTM_PL_FLAG_SYSTEM