usb: gadget: composite: don't try standard handling for non-standard requests

If a non-standard request is processed and its parameters just happen
to match those of some standard request, the logic of composite_setup()
can be fooled, so don't even try any switch cases, just go to the
proper place where unknown requests are handled.

Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>