mm/hugetlb_cgroup: remove unnecessary VM_BUG_ON_PAGE in hugetlb_cgroup_migrate()

!PageHuge(oldhpage) is implicitly checked in page_hstate() above, so we
remove this explicit one.

Link: https://lkml.kernel.org/r/20210308112809.26107-4-linmiaohe@huawei.com


Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>