Fix templatedir argument

The argument is a single template, not a directory.

Change-Id: I7a000d9ed09fd445c9ade3388193d5aa190a7809
Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
diff --git a/pimgen.py b/pimgen.py
index 306cc49..1e20aa0 100755
--- a/pimgen.py
+++ b/pimgen.py
@@ -34,7 +34,7 @@
         default=os.path.join('example', 'interfaces.yaml'),
         help='Location of interface file.'),
     parser.add_argument(
-        '-t', '--templatedir', dest='template',
+        '-t', '--template', dest='template',
         default='generated.mako.cpp',
         help='Location of mako template.')