drm: remove return value from drm_helper_mode_fill_fb_struct

Rightfully no driver ever checked this - it can't fail.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --cc drivers/gpu/drm/drm_crtc_helper.c
Simple merge

diff --cc include/drm/drm_crtc_helper.h
Simple merge