usb: gadget: f_uvc: rename a macro to avoid conflicts

When configfs is integrated, CONFIGFS_ATTR_STRUCT and CONFIGFS_ATTR_OPS
macros should be used, but the latter expects that tere is a to_f_uvc_opts
function accepting a config_item, whereas the macro being changed
can be applied to a different type of argument.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>