gxt4500: fix color order

The color order in truecolor modes is wrong. This does not affect console but
is visible e.g. in X11 which has wrong colors.

Swap blue and red colors to fix the problem.
Fixes https://forums.gentoo.org/viewtopic-t-692740-start-0.html



Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>