gfs2: 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/20251024170822.1427218-7-willy@infradead.org
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: gfs2@lists.linux.dev
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Matthew Wilcox (Oracle)

fs/gfs2/aops.c

@@ -81,8 +81,7 @@ static int gfs2_write_jdata_folio(struct folio *folio,
 	 * the page size, the remaining memory is zeroed when mapped, and
 	 * writes to that region are not written out to the file."
 	 */
-	if (folio_pos(folio) < i_size &&
-	    i_size < folio_pos(folio) + folio_size(folio))
+	if (folio_pos(folio) < i_size && i_size < folio_next_pos(folio))
 		folio_zero_segment(folio, offset_in_folio(folio, i_size),
 				folio_size(folio));