arm64/hugetlb: Use ptep_get() to get the pte value of a huge page

arm64/hugetlb: Use ptep_get() to get the pte value of a huge page

The original huge_ptep_get() on ARM64 is just a wrapper of ptep_get(),
which will not take into account any contig-PTEs dirty and access bits.
Meanwhile we will implement a new ARM64-specific huge_ptep_get()
interface in following patch, which will take into account any contig-PTEs
dirty and access bits. To keep the same efficient logic to get the pte
value, change to use ptep_get() as a preparation.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Link: https://lore.kernel.org/r/5113ed6e103f995e1d0f0c9fda0373b761bbcad2.1652496622.git.baolin.wang@linux.alibaba.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>