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 <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/video/dnfb.c

···
 {
 	int ret;
 
+	if (!MACH_IS_APOLLO)
+		return -ENODEV;
+
 	if (fb_get_options("dnfb", NULL))
 		return -ENODEV;