media: rkisp1: isp: Initialize some variables at declaration time

Initialize the src_fmt and sink_fmt variable when declaring them in
rkisp1_config_isp().

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Dafna Hirschfeld <dafna@fastmail.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>