Fixes the following smatch warning:

drivers/mtd/nand/raw/sunxi_nand.c:551 sunxi_nfc_read_byte() error: uninitialized symbol 'ret'.
Signed-off-by: NBoris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: NMiquel Raynal <miquel.raynal@bootlin.com>