video/logo: Make logo data const again

As gcc-4.1 is no longer supported, the logo data can be made const
again.  Hence revert commit 15e32524 ("fbdev: work around old
compiler bug").

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Helge Deller <deller@gmx.de>