video: fbdev: cirrusfb: Make cirrusfb_zorro_unregister() static

cirrusfb_zorro_unregister() is only used locally, hence make it static.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Helge Deller <deller@gmx.de>