drm/bridge: analogix_dp: Properly log AUX CH errors

The code in analogix_dp_transfer() that was supposed to print out:
  AUX CH error happened

Was actually dead code. That's because the previous check (whether
the interrupt status indicated any errors) would have hit for all
errors anyway.

Let's combine the two error checks so we can actually see AUX CH
errors.  We'll also downgrade the message to a warning since some of
these types of errors might be expected for some displays.  If this
gets too noisy we can downgrade again to debug.

Cc: 征增 王 <wzz@rock-chips.com>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Thierry Escande <thierry.escande@collabora.com>
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180423105003.9004-20-enric.balletbo@collabora.com