mxs_nand: Update compatible string for i.MX6SX

The iMX6SX uses compatible string "fsl,imx6sx-gpmi-nand" for gpmi
node in DTS, so update the driver for the string

Signed-off-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
diff --git a/drivers/mtd/nand/raw/mxs_nand_dt.c b/drivers/mtd/nand/raw/mxs_nand_dt.c
index 7a32b28..7efc968 100644
--- a/drivers/mtd/nand/raw/mxs_nand_dt.c
+++ b/drivers/mtd/nand/raw/mxs_nand_dt.c
@@ -25,6 +25,10 @@
 	.max_ecc_strength_supported = 40,
 };
 
+static const struct mxs_nand_dt_data mxs_nand_imx6sx_data = {
+	.max_ecc_strength_supported = 62,
+};
+
 static const struct mxs_nand_dt_data mxs_nand_imx7d_data = {
 	.max_ecc_strength_supported = 62,
 };
@@ -35,6 +39,10 @@
 		.data = (unsigned long)&mxs_nand_imx6q_data,
 	},
 	{
+		.compatible = "fsl,imx6sx-gpmi-nand",
+		.data = (unsigned long)&mxs_nand_imx6sx_data,
+	},
+	{
 		.compatible = "fsl,imx7d-gpmi-nand",
 		.data = (unsigned long)&mxs_nand_imx7d_data,
 	},