drm/pl111: make structure pl111_display_funcs static

structure pl111_display_funcs can be made static as it does not need to be
in global scope.  Fixes sparse warning:

"warning: symbol 'pl111_display_funcs' was not declared. Should it
be static?"
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Link: http://patchwork.freedesktop.org/patch/msgid/20170519110203.19417-1-colin.king@canonical.com

drivers/gpu/drm/pl111/pl111_display.c

@@ -288,7 +288,7 @@ static int pl111_display_prepare_fb(struct drm_simple_display_pipe *pipe,
 	return drm_fb_cma_prepare_fb(&pipe->plane, plane_state);
 }
 
-const struct drm_simple_display_pipe_funcs pl111_display_funcs = {
+static const struct drm_simple_display_pipe_funcs pl111_display_funcs = {
 	.check = pl111_display_check,
 	.enable = pl111_display_enable,
 	.disable = pl111_display_disable,