media: uvcvideo: Fix a typo in UVC_METATADA_BUF_SIZE

It is likely that it should be UVC_METADATA_BUF_SIZE instead.
Fix it and use it.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>