drivers: usb: udc: refine log message in udc_common.c

This refines log message in udc_common.c, including:
1. Add address of allocated net_buf info into udc_ep_buf_alloc log so
   that net_buf create/destroy can be easily monitored with calls to
   udc_ep_buf_alloc and udc_buf_destroy.
2. Add ep info into udc_ep_buf_alloc log on failure.

Signed-off-by: Chun-Chieh Li <ccli8@nuvoton.com>