OMAPDSS: OMAPFB: fix framebuffer console colors

omapfb does not currently set pseudo palette correctly for color depths
above 16bpp, making red text invisible, command like
  echo -e '\e[0;31mRED' > /dev/tty1
will display nothing in 24bpp mode.
This is because temporary variable is declared incorrectly, fix it.

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>