media: v4l2-subdev: Don't use __u32 internally

Commit a8fa5507 ("media: v4l2-subdev: Verify arguments in
v4l2_subdev_call()") and commit 374d62e7 ("media: v4l2-subdev:
Verify v4l2_subdev_call() pad config argument") introduced a few local
functions, unfortunately with arguments of type __u32, reserved for use
in Linux uAPI.  Use u32 instead.

Suggested-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Janusz Krzysztofik <jmkrzyszt@gmail.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>