pybootchartui: Fix python syntax issue

Fix:

scripts/pybootchartgui/pybootchartgui/parsing.py:134: SyntaxWarning: "is" with a literal. Did you mean "=="?
  if pid is 0:

(From OE-Core rev: 413523515dbb064680841fffa2cfdba8b2bac6f6)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit c9a6511ae618035b8efad01646e37ba28ce1e3f8)
Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/pybootchartgui/pybootchartgui/parsing.py

@@ -128,7 +128,7 @@ class Trace:
     def compile(self, writer):
 
         def find_parent_id_for(pid):
-            if pid is 0:
+            if pid == 0:
                 return 0
             ppid = self.parent_map.get(pid)
             if ppid: