UPSTREAM: mm/zsmalloc.c: fix comment for get_pages_per_zspage

(cherry-pick from commit 888fa374e625f3ee8f3cc2efebf52939d3bb6da1)

Bug: 25951511

Change-Id: I94fc95aff6dcab3999c3dcb275ca65b8cd4b3565
Signed-off-by: Yinghao Xie <yinghao.xie@sumsung.com>
Suggested-by: Minchan Kim <minchan@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>