media: uvcvideo: Use a count variable for meta_formats instead of 0 terminating

The code dealing with the 0 terminated meta_formats array is a bit klunky
especially for the uvc_meta_v4l2_enum_formats() case.

Instead of 0 terminating add an unsigned int nmeta_formats member to struct
uvc_device and use that. This leads to slightly cleaner code.

Signed-off-by: Hans de Goede <hansg@kernel.org>
Reviewed-by: Ricardo Ribalda <ribalda@chrium.org>
Tested-by: Ricardo Ribalda <ribalda@chromium.org> # Camera with MSXU_CONTROL_METADATA
Link: https://lore.kernel.org/r/20250708104622.73237-2-hansg@kernel.org


Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>