media: v4l: ioctl: Sanitize num_planes before using it

The linked commit changed s_fmt/try_fmt to fail if num_planes is bogus.
This, however, is against the spec, which mandates drivers
to return a proper num_planes value, without an error.

Replace the num_planes check and instead clamp it to a sane value,
so we still make sure we don't overflow the planes array by accident.

Fixes: 9048b2e1 ("media: v4l: ioctl: Validate num_planes before using it")

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>