mm: Fix zone->present_pages underflow
mm: Fix zone->present_pages underflow

If offlined_pages is greater than
zone->present_pages, underflow will occur.

This change will set zone->present_pages to 0 if
offlined_pages is greater.

Change-Id: I728e90c60fb7fc391de7b9c4828ab264ca38653b
Signed-off-by: Jack Cheung <19a1ebb2920ebbd9f561cd807db9c190787ca763@codeaurora.org>
(cherry picked from commit 80c201e25e8dbc00427b73d90b1527c356526442)

TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas