mm: use "GUP-fast" instead "fast GUP" in remaining comments

Let's fixup the remaining comments to consistently call that thing
"GUP-fast".  With this change, we consistently call it "GUP-fast".

Link: https://lkml.kernel.org/r/20240402125516.223131-4-david@redhat.comSigned-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Mike Rapoport (IBM) <rppt@kernel.org>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Cc: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/filemap.c

@@ -1810,7 +1810,7 @@ EXPORT_SYMBOL(page_cache_prev_miss);
  * C. Return the page to the page allocator
  *
  * This means that any page may have its reference count temporarily
- * increased by a speculative page cache (or fast GUP) lookup as it can
+ * increased by a speculative page cache (or GUP-fast) lookup as it can
  * be allocated by another user before the RCU grace period expires.
  * Because the refcount temporarily acquired here may end up being the
  * last refcount on the page, any page allocation must be freeable by

mm/khugepaged.c

@@ -1153,7 +1153,7 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
 	 * huge and small TLB entries for the same virtual address to
 	 * avoid the risk of CPU bugs in that area.
 	 *
-	 * Parallel fast GUP is fine since fast GUP will back off when
+	 * Parallel GUP-fast is fine since GUP-fast will back off when
 	 * it detects PMD is changed.
 	 */
 	_pmd = pmdp_collapse_flush(vma, address, pmd);