media: stm32-dcmi: do not fall into error on buffer starvation

Return silently instead of falling into error when running
out of available buffers when restarting capture.
Capture will be restarted when new buffers will be
provided by V4L2 client.

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+samsung@kernel.org>