m68k: fix comment typo diable -> disable.

The below patch fixes a typo "diable" to "disable". Please let me know if this
is correct or not.

Signed-off-by: Justin P. Mattock <justinmattock@gmail.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>