drm/sun4i: Fix polarity configuration for DW HDMI PHY

Current polarity configuration code is cleary wrong since it compares
same flag two times. However, even if flag name is fixed, it won't work
well for resolutions which have one polarity positive and another
negative.

Fix that by properly set each bit according to each polarity. Since
those two bits are not described in any documentation, relationships
were obtained by experimentation.

Fixes: b7c7436a

 ("drm/sun4i: Implement A83T HDMI driver")

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180301213442.16677-10-jernej.skrabec@siol.net