mm/shmem.c: Use new form of *@param in kernel-doc

Use the form of *@param which kernel-doc recognizes now.
This resolves the warnings from "make htmldocs" as reported in [1].

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Link: [1] https://lore.kernel.org/r/20240223153636.41358be5@canb.auug.org.au/
Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>

mm/shmem.c

@@ -2152,8 +2152,8 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
  * There is no need to reserve space before calling folio_mark_dirty().
  *
  * When no folio is found, the behavior depends on @sgp:
- *  - for SGP_READ, *foliop is %NULL and 0 is returned
- *  - for SGP_NOALLOC, *foliop is %NULL and -ENOENT is returned
+ *  - for SGP_READ, *@foliop is %NULL and 0 is returned
+ *  - for SGP_NOALLOC, *@foliop is %NULL and -ENOENT is returned
  *  - for all other flags a new folio is allocated, inserted into the
  *    page cache and returned locked in @foliop.
  *