media: atmel: atmel-isc: fix INIT_WORK misplacement

In case the completion function failes, unbind will be called
which will call cancel_work for awb_work.
This will trigger a WARN message from the workqueue.
To avoid this, move the INIT_WORK call at the start of the completion
function. This way the work is always initialized, which corresponds
to the 'always canceled' unbind code.

Fixes: 93d4a26c ("[media] atmel-isc: add the isc pipeline function")

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>