ecryptfs: Convert ecryptfs_write() to use a folio

Remove ecryptfs_get_locked_page() and call read_mapping_folio()
directly.  Use the folio throught this function.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Link: https://lore.kernel.org/r/20241025190822.1319162-6-willy@infradead.org


Reviewed-by: Pankaj Raghav <p.raghav@samsung.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>