aries | p1: staging: zsmalloc: access page->private by using page_private macro

Signed-off-by: Sunghan Suh <sunghan.suh@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Humberto Borba <humberos@gmail.com>

Change-Id: I832951b744ec874ce4a2b898dfaeea4ed29a8b88