tools: efivar.py without arguments

When tools: efivar.py is called without arguments an error occurs:

Traceback (most recent call last):
  File "tools/efivar.py", line 380, in <module>
    main()
  File "tools/efivar.py", line 360, in main
    args.func(args)
AttributeError: 'Namespace' object has no attribute 'func'

Show the online help if the arguments do not specify a function.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>

tools/efivar.py

@@ -357,7 +357,10 @@ def main():
     signp.set_defaults(func=cmd_sign)
 
     args = ap.parse_args()
-    args.func(args)
+    if hasattr(args, "func"):
+        args.func(args)
+    else:
+        ap.print_help()
 
 def group(a, *ns):
     for n in ns: