hugetlb: replace the obsolete hugetlb_instantiation_mutex in the comments

After commit 8382d914 ("mm, hugetlb: improve page-fault
scalability"), the hugetlb_instantiation_mutex lock had been replaced by
hugetlb_fault_mutex_table to serializes faults on the same logical page.

Thus update the obsolete hugetlb_instantiation_mutex related comments.

Link: https://lkml.kernel.org/r/4b3febeae37455ff7b74aa0aad16cc6909cf0926.1634797639.git.baolin.wang@linux.alibaba.comSigned-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Michal Hocko <mhocko@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/hugetlb.c

@@ -5014,7 +5014,7 @@ static void unmap_ref_private(struct mm_struct *mm, struct vm_area_struct *vma,
 
 /*
  * Hugetlb_cow() should be called with page lock of the original hugepage held.
- * Called with hugetlb_instantiation_mutex held and pte_page locked so we
+ * Called with hugetlb_fault_mutex_table held and pte_page locked so we
  * cannot race with other handlers or page migration.
  * Keep the pte_same checks anyway to make transition from the mutex easier.
  */