drm/bridge/analogix/anx78xx: Cleanup on error in anx78xx_bridge_attach()

Just another issue I noticed while correcting usages of
drm_dp_aux_init()/drm_dp_aux_register() around the tree. If any of the
steps in anx78xx_bridge_attach() fail, we end up leaking resources. So,
let's fix that (and fix leaking a DP AUX adapter in the process) by
unrolling on errors.

Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210219215326.2227596-10-lyude@redhat.com