mm/shmem.c: suppress shift warning

mm/shmem.c:1948 shmem_getpage_gfp() warn: should '(((1) << 12) / 512) << folio_order(folio)' be a 64 bit type?

On i386, so an unsigned long is 32-bit, but i_blocks is a 64-bit blkcnt_t.
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Jessica Clarke <jrtc27@jrtc27.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/shmem.c

@@ -1945,7 +1945,7 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
 
 	spin_lock_irq(&info->lock);
 	info->alloced += folio_nr_pages(folio);
-	inode->i_blocks += BLOCKS_PER_PAGE << folio_order(folio);
+	inode->i_blocks += (blkcnt_t)BLOCKS_PER_PAGE << folio_order(folio);
 	shmem_recalc_inode(inode);
 	spin_unlock_irq(&info->lock);
 	alloced = true;