Staging: rtl8712: Remove unnecessary cast on void pointer

The conversion from void pointer to any other pointer type is guaranteed
by the C programming language.

The semantic patch used to find this:

@r@
expression x;
void* e;
type T;
identifier f;
@@

(
  *((T *)e)
|
  ((T *)x)[...]
|
  ((T *)x)->f
|
- (T *)
  e
)

Signed-off-by: Lucas Tanure <tanure@linux.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>