neofb: Fix pseudo_palette array overrun in neofb_setcolreg

The pseudo_palette has room for 16 entries only, but in truecolor mode, it
attempts to write 256.

Signed-off-by: Antonino Daplas <adaplas@gmail.com>
Acked-by: Tero Roponen <teanropo@jyu.fi>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>