waftools: openocd: fix OSError errno access

Python 3 exposes errno property.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>

waftools/openocd.py

@@ -71,7 +71,7 @@ def _is_openocd_running():
         s.close()
     except socket.error as e:
         s.close()
-        return e[0] == errno.EADDRINUSE
+        return e.errno == errno.EADDRINUSE
     return False