mtd: rawnand: stm32_fmc2: fix a buffer overflow

The chip select defined in the device tree could only be 0 or 1.

Signed-off-by: Christophe Kerello <christophe.kerello@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/drivers/mtd/nand/raw/stm32_fmc2_nand.c b/drivers/mtd/nand/raw/stm32_fmc2_nand.c
index 3306bd8..2929acf 100644
--- a/drivers/mtd/nand/raw/stm32_fmc2_nand.c
+++ b/drivers/mtd/nand/raw/stm32_fmc2_nand.c
@@ -846,7 +846,7 @@
 	}
 
 	for (i = 0; i < nand->ncs; i++) {
-		if (cs[i] > FMC2_MAX_CE) {
+		if (cs[i] >= FMC2_MAX_CE) {
 			pr_err("Invalid reg value: %d\n",
 			       nand->cs_used[i]);
 			return -EINVAL;