usb: gadget: uvc: configfs: Fix operation on big endian platforms

USB descriptors are stored in little endian, requiring the use of
conversion macros. Those macros are incorrectly used for values stored
in native endian structures within the driver. Operation on big endian
platforms is thus broken. Fix it by removing the conversion macros where
they're not needed.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Tested-by: Paul Elder <paul.elder@ideasonboard.com>