net: dsa: Test array index before use

port_index is used an index into an array, and this information comes
from Device Tree, make sure that port_index is not equal to the array
size before using it. Move the check against port_index earlier in the
loop.

Fixes: 5e95329b701c: ("dsa: add device tree bindings to register DSA switches")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/dsa.c

@@ -642,6 +642,8 @@ static int dsa_of_probe(struct device *dev)
 				continue;
 
 			port_index = be32_to_cpup(port_reg);
+			if (port_index >= DSA_MAX_PORTS)
+				break;
 
 			port_name = of_get_property(port, "label", NULL);
 			if (!port_name)
@@ -666,8 +668,6 @@ static int dsa_of_probe(struct device *dev)
 					goto out_free_chip;
 			}
 
-			if (port_index == DSA_MAX_PORTS)
-				break;
 		}
 	}