m68k: dnfb doesnt check for Apollo

The Apollo frame buffer device driver (dnfb) doesn't check whether it's
actually running on Apollo hardware, causing a crash if it isn't.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>