media: allegro: use handler_setup to configure channel

v4l2_ctrl_handler_setup() calls s_ctrl for all controls of the handler.
This ensures that the channel is initialized using the default values of
the v4l2-ctrls.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>