mm: hugetlb: use get_page_foll() in follow_hugetlb_page()

mm: hugetlb: use get_page_foll() in follow_hugetlb_page()

get_page_foll() is more optimal and is always safe to use under the PT
lock.  More so for hugetlbfs as there's no risk of race conditions with
split_huge_page regardless of the PT lock.

Signed-off-by: Andrea Arcangeli <[email protected]>
Tested-by: Khalid Aziz <[email protected]>
Cc: Pravin Shelar <[email protected]>
Cc: Greg Kroah-Hartman <[email protected]>
Cc: Ben Hutchings <[email protected]>
Cc: Christoph Lameter <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Minchan Kim <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>