xfs: Use folio_next_pos()

This is one instruction more efficient than open-coding folio_pos() +
folio_size().  It's the equivalent of (x + y) << z rather than
x << z + y << z.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://patch.msgid.link/20251024170822.1427218-10-willy@infradead.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Carlos Maiolino <cem@kernel.org>
Cc: linux-xfs@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Matthew Wilcox (Oracle)

fs/xfs/scrub/xfarray.c

@@ -834,7 +834,7 @@ xfarray_sort_scan(
 		si->first_folio_idx = xfarray_idx(si->array,
 				folio_pos(si->folio) + si->array->obj_size - 1);
 
-		next_pos = folio_pos(si->folio) + folio_size(si->folio);
+		next_pos = folio_next_pos(si->folio);
 		si->last_folio_idx = xfarray_idx(si->array, next_pos - 1);
 		if (xfarray_pos(si->array, si->last_folio_idx + 1) > next_pos)
 			si->last_folio_idx--;

fs/xfs/xfs_aops.c

@@ -271,7 +271,7 @@ xfs_discard_folio(
 	 * folio itself and not the start offset that is passed in.
 	 */
 	xfs_bmap_punch_delalloc_range(ip, XFS_DATA_FORK, pos,
-				folio_pos(folio) + folio_size(folio), NULL);
+				folio_next_pos(folio), NULL);
 }
 
 /*