drm/atomic: Use new iterator macros in drm_atomic_helper_wait_for_flip_done

for_each_obj_in_state is about to be removed, so use the correct new
iterator macro.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: David Airlie <airlied@linux.ie>
Link: http://patchwork.freedesktop.org/patch/msgid/20170712081344.25495-5-maarten.lankhorst@linux.intel.com


[mlankhorst: Based on danvet's feedback, only apply first hunk and rename crtc_state variable to unused]
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>