drm/sun4i: tcon: Change vertical total size computation inconsistency

Both TCON channels need to have the resolution doubled, since the size the
hardware is going to use is whatever we put in the register divided by two.

However, we handle it differently for the two channels: in the channel 0,
our register access macro does the multiplication of the value passed as
paremeter, while in the channel 1, the macro doesn't do this, and we need
to do it before calling it.

Make this consistent by aligning the channel 0 with the channel 1
behaviour.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>