Use appropriate accessor function to set compound page destructor
function.

Cc:  William Irwin <wli@holomorphy.com>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Acked-by: Adam Litke <agl@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>