Staging: gdx724x: gdm_mux: Remove explicit cast

Compiler can typecast variables implicitly so, explicit type cast is not
required and should be removed.
Semantic patch used:

@@
type T;
T e;
identifier x;
@@

* T x = (T)e;

Signed-off-by: Shivani Bhardwaj <shivanib134@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>