ext4: Make mpage_journal_page_buffers use folio

This patch converts mpage_journal_page_buffers() to use folio and also
removes the PAGE_SIZE assumption.

Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://lore.kernel.org/r/ebc3ac80e6a54b53327740d010ce684a83512021.1684122756.git.ritesh.list@gmail.com


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