usb: Compile with -Wextra

-Wextra enables a bunch of rather useful checks which this fixes with
one exception of -Wunused-parameter - this fixes it for debug macros only
and leave the rest for the future as more functional change is needed.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
Changes:
v2:
* updated debug macros to fix -Wunused-parameter

---

These are not fixed:
 ====== Building common libraries ======
        [CC]    usb-core.o
        [CC]    usb-ohci.o
        [CC]    usb-hid.o
        [CC]    usb-xhci.o
/home/aik/p/slof/lib/libusb/usb-core.c: In function ‘usb_set_address’:
/home/aik/p/slof/lib/libusb/usb-core.c:244:58: warning: unused parameter ‘port’ [-Wunused-parameter]
 static int usb_set_address(struct usb_dev *dev, uint32_t port)
                                                          ^~~~
/home/aik/p/slof/lib/libusb/usb-xhci.c: In function ‘xhci_send_enable_slot’:
/home/aik/p/slof/lib/libusb/usb-xhci.c:353:67: warning: unused parameter ‘port’ [-Wunused-parameter]
 static void xhci_send_enable_slot(struct xhci_hcd *xhcd, uint32_t port)
                                                                   ^~~~
/home/aik/p/slof/lib/libusb/usb-ohci.c: In function ‘ohci_dump_regs’:
/home/aik/p/slof/lib/libusb/usb-ohci.c:42:46: warning: unused parameter ‘regs’ [-Wunused-parameter]
 static void ohci_dump_regs(struct ohci_regs *regs)
                                              ^~~~
/home/aik/p/slof/lib/libusb/usb-core.c: In function ‘usb_handle_device’:
/home/aik/p/slof/lib/libusb/usb-core.c:444:80: warning: unused parameter ‘cfg’ [-Wunused-parameter]
 static int usb_handle_device(struct usb_dev *dev, struct usb_dev_config_descr *cfg,
                                                                                ^~~
/home/aik/p/slof/lib/libusb/usb-xhci.c: In function ‘fill_setup_trb’:
/home/aik/p/slof/lib/libusb/usb-xhci.c:1026:13: warning: unused parameter ‘size’ [-Wunused-parameter]
    uint32_t size)
             ^~~~
/home/aik/p/slof/lib/libusb/usb-xhci.c: In function ‘xhci_transfer_bulk’:
/home/aik/p/slof/lib/libusb/usb-xhci.c:1217:60: warning: unused parameter ‘td’ [-Wunused-parameter]
 static int xhci_transfer_bulk(struct usb_pipe *pipe, void *td, void *td_phys,
                                                            ^~
/home/aik/p/slof/lib/libusb/usb-xhci.c:1217:70: warning: unused parameter ‘td_phys’ [-Wunused-parameter]
 static int xhci_transfer_bulk(struct usb_pipe *pipe, void *td, void *td_phys,
                                                                      ^~~~~~~
/home/aik/p/slof/lib/libusb/usb-xhci.c: In function ‘xhci_get_pipe_intr’:
/home/aik/p/slof/lib/libusb/usb-xhci.c:1364:22: warning: unused parameter ‘len’ [-Wunused-parameter]
    char *buf, size_t len)
                      ^~~