drm/fb-helper: Remove unnecessary list empty check in drm_fb_helper_debug_enter()

The following list empty check is unnecessary because we would still do nothing
real and return 'val' if my_list is empty.

if (list_empty(&my_list))
	return val;

list_for_each_entry(pos, &my_list, member) {
	...
}

return val;

This patch removes the unnecessary check in drm_fb_helper_debug_enter().

Signed-off-by: Liu Ying <Ying.Liu@freescale.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>