m68k: remove duplicate asm offset for task thread.info

We have a duplicate name and definition for the offset of the thread.info
struct within the task struct in our asm-offsets.c code. Remove one of them,
and consolidate to use a single define, TASK_INFO.

Signed-off-by: Greg Ungerer <gerg@uclinux.org>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>