gianfar: Fix overflow check and return value for gfar_get_cls_all()

This function may currently fill one entry beyond the end of the
array it is given.  It also doesn't return an error code in case
it does detect overflow.
Signed-off-by: NBen Hutchings <bhutchings@solarflare.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/gianfar_ethtool.c

@@ -1669,10 +1669,10 @@ static int gfar_get_cls_all(struct gfar_private *priv,
 	u32 i = 0;
 
 	list_for_each_entry(comp, &priv->rx_list.list, list) {
-		if (i <= cmd->rule_cnt) {
-			rule_locs[i] = comp->fs.location;
-			i++;
-		}
+		if (i == cmd->rule_cnt)
+			return -EMSGSIZE;
+		rule_locs[i] = comp->fs.location;
+		i++;
 	}
 
 	cmd->data = MAX_FILER_IDX;