hugetlbfs: make hugepage size conversion more readable

hugetlbfs: make hugepage size conversion more readable

The calculation 1U << (h->order + PAGE_SHIFT - 10) is actually equal to
(PAGE_SHIFT << (h->order)) >> 10.  So we can make it more readable by
replace it with huge_page_size(h) >> 10.

Link: https://lkml.kernel.org/r/20210122083141.24548-1-linmiaohe@huawei.com
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>