patman: Make exception handling python 3.x safe

Syntax for exception handling is a little more strict in python 3.x.
Convert all uses to a form accepted by both python 2.x & python 3.x.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Acked-by: Simon Glass <sjg@chromium.org>

tools/patman/cros_subprocess.py

@@ -166,7 +166,7 @@ class Popen(subprocess.Popen):
         while read_set or write_set:
             try:
                 rlist, wlist, _ = select.select(read_set, write_set, [], 0.2)
-            except select.error, e:
+            except select.error as e:
                 if e.args[0] == errno.EINTR:
                     continue
                 raise