ext2: Remove reference to bh->b_page

Buffer heads are attached to folios, not to pages.  Also
flush_dcache_page() is now deprecated in favour of flush_dcache_folio().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20250213182045.2131356-1-willy@infradead.org