Staging: rtl8723bs/os_dep: Remove typecast in kfree

Remove typecast of pointer in kfree((u8 *)pdvobj) as
it is not needed.

Found using the following Coccinelle semantic patch:
@@
identifier x;
type t;
@@

-kfree((t *)x)
+kfree(x)

Signed-off-by: Meghana Madhyastha <meghana.madhyastha@gmail.com>
Acked-by: Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>