After we acquired all generic modeset locks in drm_modeset_lock_all, it's
unsafe acquire any other so just mark acquisition as done.

Atomic drivers shouldn't use drm_modeset_lock_all.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180221152331.9212-1-maarten.lankhorst@linux.intel.comReviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Harry Wentland <harry.wentland@amd.com>