mtd: rawnand: fsmc: Stop using chip->read_buf()

chip->read_buf is left unassigned since commit 4da712e7 ("mtd: nand:
fsmc: use ->exec_op()"), leading to a NULL pointer dereference when it's
called from fsmc_read_page_hwecc(). Fix that by using the appropriate
helper to read data out of the NAND.

Fixes: 4da712e7 ("mtd: nand: fsmc: use ->exec_op()")
Cc: <stable@vger.kernel.org>
Signed-off-by: NBoris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: NMiquel Raynal <miquel.raynal@bootlin.com>

drivers/mtd/nand/raw/fsmc_nand.c

@@ -741,7 +741,7 @@ static int fsmc_read_page_hwecc(struct mtd_info *mtd, struct nand_chip *chip,
 	for (i = 0, s = 0; s < eccsteps; s++, i += eccbytes, p += eccsize) {
 		nand_read_page_op(chip, page, s * eccsize, NULL, 0);
 		chip->ecc.hwctl(mtd, NAND_ECC_READ);
-		chip->read_buf(mtd, p, eccsize);
+		nand_read_data_op(chip, p, eccsize, false);
 
 		for (j = 0; j < eccbytes;) {
 			struct mtd_oob_region oobregion;