usb: gadget: uvc: Fix coding style issues introduced by SS support

Let's keep the code consistent, people might want to read it.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Bhupesh Sharma <bhupesh.sharma@st.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>