spl: nand: simple: replace readb() with chip specific read_buf()

Some NAND controllers define custom functions to read data out,
respect this in order to correctly support bad block handling in
simple SPL NAND framework.

NAND controller specific read_buf() is used even to read 1 byte in
case of connected 8-bit NAND device, it turns out that read_byte()
may become outdated.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Cc: Tom Rini <trini@konsulko.com>
Cc: Tom Warren <twarren@nvidia.com>
Acked-by: Scott Wood <scottwood@freescale.com>

drivers/mtd/nand/nand_spl_simple.c

@@ -115,6 +115,7 @@ static int nand_command(int block, int page, uint32_t offs,
 static int nand_is_bad_block(int block)
 {
 	struct nand_chip *this = mtd.priv;
+	u_char bb_data[2];
 
 	nand_command(block, 0, CONFIG_SYS_NAND_BAD_BLOCK_POS,
 		NAND_CMD_READOOB);
@@ -123,10 +124,12 @@ static int nand_is_bad_block(int block)
 	 * Read one byte (or two if it's a 16 bit chip).
 	 */
 	if (this->options & NAND_BUSWIDTH_16) {
-		if (readw(this->IO_ADDR_R) != 0xffff)
+		this->read_buf(&mtd, bb_data, 2);
+		if (bb_data[0] != 0xff || bb_data[1] != 0xff)
 			return 1;
 	} else {
-		if (readb(this->IO_ADDR_R) != 0xff)
+		this->read_buf(&mtd, bb_data, 1);
+		if (bb_data[0] != 0xff)
 			return 1;
 	}