fbdev: sa1100fb: mark sa1100fb_init() static

This is a global function that is only referenced as an initcall. This causes
a warning:

drivers/video/fbdev/sa1100fb.c:1218:12: error: no previous prototype for 'sa1100fb_init' [-Werror=missing-prototypes]

Make it static instead.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Helge Deller <deller@gmx.de>