udf: Convert udf_write_begin() to use a folio

Use the folio APIs throughout instead of the deprecated page APIs.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <20240417150416.752929-3-willy@infradead.org>