drm/sun4i: sun8i_csc: Simplify register writes

It turns out addition of 0x200 to constant parts (+0.5) is not really
necessary. Besides, we can consider that before and fix value in CSC
matrix.

This simplifies register writes quiet a bit.

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/20190713120346.30349-3-jernej.skrabec@siol.net