media: redrat3: use int type to store negative error codes

Change "ret" from u8 to int type in redrat3_enable_detector() to store
negative error codes or zero returned by redrat3_send_cmd() and
usb_submit_urb() - this better aligns with the coding standards and
maintains code consistency.

No effect on runtime.

Signed-off-by: Qianfeng Rong <rongqianfeng@vivo.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>