mtd: rawnand: atmel: Use nand_prog_page_end_op()

The nand_prog_page_end_op() sequence is open-coded in
atmel_hsmc_nand_pmecc_write_pg(). Let's use the generic helper here.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200720131356.1579073-5-tudor.ambarus@microchip.com