Add function that returns the control name. Allows this to be used in
places where the normal v4l2_ctrl_query_fill() function cannot be
used (e.g. uvc).
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>