mm/hugetlb: use already existing interface huge_page_shift

Use the already existing interface huge_page_shift instead of h->order +
PAGE_SHIFT.

Signed-off-by: Wanpeng Li <liwanp@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index 77fdd2c..4210549 100644
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c
@@ -357,7 +357,7 @@
 int alloc_bootmem_huge_page(struct hstate *hstate)
 {
 	struct huge_bootmem_page *m;
-	int idx = shift_to_mmu_psize(hstate->order + PAGE_SHIFT);
+	int idx = shift_to_mmu_psize(huge_page_shift(hstate));
 	int nr_gpages = gpage_freearray[idx].nr_gpages;
 
 	if (nr_gpages == 0)