patman: check git format.subjectprefix setting when generate patches prefix

For the local project, we may specified format.subjectprefix setting.
Then the patch will be formated as [Project_prefix][PATCH].
But patman will not check this setting. It will remove the
format.subjectprefix.

So This patch will let patman check this setting and add it as a
project prefix.

Signed-off-by: Josh Wu <josh.wu@atmel.com>
Acked-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>
diff --git a/tools/patman/series.py b/tools/patman/series.py
index 60ebc76..a17a7d1 100644
--- a/tools/patman/series.py
+++ b/tools/patman/series.py
@@ -254,6 +254,12 @@
         Return:
             Patch string, like 'RFC PATCH v5' or just 'PATCH'
         """
+        git_prefix = gitutil.GetDefaultSubjectPrefix()
+        if git_prefix:
+	    git_prefix = '%s][' % git_prefix
+        else:
+            git_prefix = ''
+
         version = ''
         if self.get('version'):
             version = ' v%s' % self['version']
@@ -262,4 +268,4 @@
         prefix = ''
         if self.get('prefix'):
             prefix = '%s ' % self['prefix']
-        return '%sPATCH%s' % (prefix, version)
+        return '%s%sPATCH%s' % (git_prefix, prefix, version)