drm/tegra: Get ref for DP AUX channel, not its ddc adapter

While we're taking a reference of the DDC adapter for a DP AUX channel in
tegra_sor_probe() because we're going to be using that adapter with the
SOR, now that we've moved where AUX registration happens the actual device
structure for the DDC adapter isn't initialized yet. Which means that we
can't really take a reference from it to try to keep it around anymore.

This should be fine though, because we can just take a reference of its
parent instead.

v2:
* Avoid calling i2c_put_adapter() in tegra_output_remove() for eDP/DP cases

Signed-off-by: Lyude Paul <lyude@redhat.com>
Fixes: 39c17ae6

 ("drm/tegra: Don't register DP AUX channels before connectors")
Cc: Lyude Paul <lyude@redhat.com>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Jonathan Hunter <jonathanh@nvidia.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-tegra@vger.kernel.org
Signed-off-by: Thierry Reding <treding@nvidia.com>