ext4: Use a folio in ext4_da_write_begin()

Remove a few calls to compound_head().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://lore.kernel.org/r/20230324180129.1220691-23-willy@infradead.org


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