V4L/DVB (6098): ivtv: kzalloc() returns void pointer, no need to cast

Since kzalloc() returns a void pointer, we don't need to cast the
return value in drivers/media/video/ivtv/ivtv-queue.c

Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>