media: i2c: ov9282: Fix missing documentation in structures

Fix missing documentation entries for members of structures,
as flagged by smatch.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>