drm: sun4i: hdmi: Fix inverted HPD result

When the extra HPD polling in sun4i_hdmi was removed, the result of
HPD was accidentally inverted.

Fix this by inverting the check.

Fixes: bda8eaa6

 ("drm: sun4i: hdmi: Remove extra HPD polling")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Tested-by: Mans Rullgard <mans@mansr.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20200711011030.21997-1-wens@kernel.org