addons/cppcheckdata.py: Fix missing self, and wrong assignment. (#1919)

I am not sure but it looks like "self." is missing here.
And the attribute "inconclusive" is initialized as a "bool", so i guess
"True" should be assigned here?

addons/cppcheckdata.py

@@ -491,11 +491,11 @@ class ValueFlow:
             if self.condition:
                 self.condition = int(self.condition)
             if element.get('known'):
-                valueKind = 'known'
+                self.valueKind = 'known'
             elif element.get('possible'):
-                valueKind = 'possible'
+                self.valueKind = 'possible'
             if element.get('inconclusive'):
-                inconclusive = 'known'
+                self.inconclusive = True
 
     def __init__(self, element):
         self.Id = element.get('id')