With some of the stricter type checking in KUnit's EXPECT macros
removed, a cast in cmdline_kunit is no longer required.

Remove the unnecessary cast, using NULL instead of (int *) to make it
clearer.
Signed-off-by: NDavid Gow <davidgow@google.com>
Acked-by: NAndy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: NBrendan Higgins <brendanhiggins@google.com>
Signed-off-by: NShuah Khan <skhan@linuxfoundation.org>