media: v4l2-ctrls.c: fix broken auto cluster handling

When you switch from auto to manual mode for an auto-cluster (e.g.
autogain+gain controls), then the current HW value has to be copied
to the current control value. However, has_changed was never set to
true, so new_to_cur didn't actually copy this value.

Reported-by: Hugues FRUCHET <hugues.fruchet@st.com>
Tested-by: Hugues FRUCHET <hugues.fruchet@st.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>