mtd: rawnand: atmel: Check return values for nand_read_data_op

In atmel_nand_pmecc_read_pg(), nand_read_data_op() is called twice
without the return values being checked for errors. Add these checks.

Signed-off-by: Alex Dewar <alex.dewar90@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200914214245.14626-1-alex.dewar90@gmail.com