drm/tegra: Use __drm_atomic_helper_reset_connector for subclassing connector state, v2.

Changes since v1:
- Do not reset if state allocation fails.

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Acked-by: Thierry Reding <treding@nvidia.com> #irc
Link: http://patchwork.freedesktop.org/patch/msgid/1451908400-25147-3-git-send-email-maarten.lankhorst@linux.intel.com


Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>