`clipcount' is from userspace and thus needs validation.  Otherwise,
a large `clipcount' could overflow the vmalloc() size, leading to
out-of-bounds access.

| setup_window()
| zoran_s_fmt_vid_overlay()
| __video_do_ioctl()
| video_ioctl2()

Use 2048 as the maximum `clipcount'.  Also change the corresponding
parameter type to `unsigned int'.
Signed-off-by: Xi Wang <xi.wang@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>