media: uvcvideo: New macro uvc_trace_cont

Remove all the duplicated code around printk(KERN_CONT, with a new macro.

Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>