The `V4L2BufferCache` type is not thread-safe. Its `lastUsedCounter_`
member is not used in contexts where its atomicity would matter.
So it does not need to be have an atomic type.
Signed-off-by: Barnabás Pőcze <barnabas.pocze@ideasonboard.com>
Reviewed-by: Jacopo Mondi <jacopo.mondi@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>