ext4/move_extent: use folio_next_pos()

ext4/move_extent: use folio_next_pos()

A series of patches such as commit 60a70e61430b ("mm: Use
folio_next_pos()") replace folio_pos() + folio_size() by
folio_next_pos().  The former performs x << z + y << z while
the latter performs (x + y) << z, which is slightly more
efficient. This case was not taken into account, perhaps
because the argument is not named folio.

The change was performed using the following Coccinelle
semantic patch:

@@
expression folio;
@@

- folio_pos(folio) + folio_size(folio)
+ folio_next_pos(folio)

Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20260222125049.1309075-1-Julia.Lawall@inria.fr
Signed-off-by: Theodore Ts'o <tytso@mit.edu>