media: ov5640: Update last busy timestamp to reset autosuspend timer

Otherwise autosuspend delay doesn't work and power is cut off
immediately as device is freed.

Signed-off-by: Andrey Skvortsov <andrej.skvortzov@gmail.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>