patman: don't pick changes while processing patches

We already got all changes from git log output and the comment
to the ProcessLine function clearly states that 'patch' mode
is not for scanning tags.

Signed-off-by: Ilya Yanok <ilya.yanok@cogentembedded.com>

tools/patman/patchstream.py

@@ -214,7 +214,8 @@ class PatchStream:
                 self.in_change = 0
                 out = self.ProcessLine(line)
             else:
-                self.series.AddChange(self.in_change, self.commit, line)
+                if self.is_log:
+                    self.series.AddChange(self.in_change, self.commit, line)
             self.skip_blank = False
 
         # Detect Series-xxx tags