ALSA: ctxfi: removed typecast to (struct hw *)

the previous patch of the series has converted the void * to
struct hw * . Now this patch removes the typecasting to (struct hw *)
which is not needed any more.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>