drm/bridge: ti-sn65dsi86: Clear old error bits before AUX transfers

drm/bridge: ti-sn65dsi86: Clear old error bits before AUX transfers

[ Upstream commit baef4d56195b6d6e0f681f6eac03d8c6db011d34 ]

The AUX channel transfer error bits in the status register are latched
and need to be cleared.  Clear them before doing our transfer so we
don't see old bits and get confused.

Without this patch having a single failure would mean that all future
transfers would look like they failed.

Fixes: b814ec6d4535 ("drm/bridge: ti-sn65dsi86: Implement AUX channel")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200508163314.1.Idfa69d5d3fc9623083c0ff78572fea87dccb199c@changeid
Signed-off-by: Sasha Levin <sashal@kernel.org>