drm: mxsfb: Make local symbol mxsfb_funcs static

Fixes the following sparse warning:

drivers/gpu/drm/mxsfb/mxsfb_drv.c:129:38: warning:
 symbol 'mxsfb_funcs' was not declared. Should it be static?
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/20170205160538.16594-1-weiyj.lk@gmail.com

drivers/gpu/drm/mxsfb/mxsfb_drv.c

@@ -126,7 +126,7 @@ static int mxsfb_pipe_prepare_fb(struct drm_simple_display_pipe *pipe,
 	return drm_fb_cma_prepare_fb(&pipe->plane, plane_state);
 }
 
-struct drm_simple_display_pipe_funcs mxsfb_funcs = {
+static struct drm_simple_display_pipe_funcs mxsfb_funcs = {
 	.enable		= mxsfb_pipe_enable,
 	.disable	= mxsfb_pipe_disable,
 	.update		= mxsfb_pipe_update,