matroxfb: color setting fixes fix

Remove more code that writes to cmap[16].

Signed-off-by: Antonino Daplas <adaplas@gmail.com>
Acked-by: Petr Vandrovec <VANDROVE@vc.cvut.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>