ext4: Use a folio iterator in __read_end_io()

Iterate once per folio, not once per page.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://lore.kernel.org/r/20230324180129.1220691-27-willy@infradead.org


Signed-off-by: Theodore Ts'o <tytso@mit.edu>