ath9k: remove cast to void pointer

casting to void pointer from any pointer type and vice-versa is done
implicitly and therefore casting is not needed in such a case.

Done using Coccinellle.
Semantic Patch used :

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

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


Signed-off-by: Himanshu Jha <himanshujha199640@gmail.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>