media: stm32-dcmi: improve error trace points

Fix some missing "\n".
Trace error returned by subdev streamon/streamoff.
Remove extra "0x" unneeded with %pad formatter.

Signed-off-by: Hugues Fruchet <hugues.fruchet@st.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>