m68k: fix access_ok for coldfire

commit 26509034 upstream.

While most m68k platforms use separate address spaces for user
and kernel space, at least coldfire does not, and the other
ones have a TASK_SIZE that is less than the entire 4GB address
range.

Using the default implementation of __access_ok() stops coldfire
user space from trivially accessing kernel memory.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: stable@vger.kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>