rds module: Fix undeclared reference to "params" when setting password in

modify mode.

library/cloud/rds

@@ -370,6 +370,9 @@ def main():
         else:
             return 'vpc_security_groups'
 
+    # Package up the optional parameters
+    params = {}
+
     # Validate parameters for each command
     if command == 'create':
         required_vars = [ 'instance_name', 'db_engine', 'size', 'instance_type', 'username', 'password' ]
@@ -413,9 +416,6 @@ def main():
         if module.params.get(v):
             module.fail_json(msg = str("Parameter %s invalid for %s command" % (v, command)))
 
-    # Package up the optional parameters
-    params = {}
-
     if db_engine:
         params["engine"] = db_engine