The iSight sends non-UVC status events through the interrupt endpoint. Those
invalid events are reported to the kernel log, resulting in a log flood.

Only log the events when the UVC_TRACE_STATUS flag is set.
Signed-off-by: Laurent Pinchart <laurent.pinchart@skynet.be>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>