udc: core: Fix use after free issue

In usb_ep_free_request request is freed in gadget driver
and passed to trace_event_usb_ep_free_request, which can
result in invalid memory access.
Fix this by first calling trace_event_usb_ep_free_request
and then free the request

Signed-off-by: Sai Krishna Juturi <jsaikrishna@codeaurora.org>
Change-Id: I3f6e4f02159b0789332818c5f181b1d1586edb17