media: rkisp1: Configure quantization using ISP source pad

The rkisp1_config_isp() function uses the format on the sink pad of the
ISP to configure quantization at the output of the ISP. This is
incorrect, as hinted by the src_frm variable name that stores the
format. Fix it by using the source pad.

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>