hw/usb/hcd-xhci: Fix extraneous format-truncation error on 32-bit hosts

hw/usb/hcd-xhci: Fix extraneous format-truncation error on 32-bit hosts

For some reason the assert() added in commit ccb799313a5
("hw/usb: avoid format truncation warning when formatting
port name") does not fix when building with GCC 10.

KISS and expand the buffer by 4 bytes to silent the following
error when using GCC 10.2.1 on Fedora 33:

  hw/usb/hcd-xhci.c: In function 'usb_xhci_realize':
  hw/usb/hcd-xhci.c:3309:54: error: '%d' directive output may be truncated writing between 1 and 8 bytes into a region of size 5 [-Werror=format-truncation=]
   3309 |             snprintf(port->name, sizeof(port->name), "usb2 port #%d", i+1);
        |                                                      ^~~~~~~~~~~~~~~
  hw/usb/hcd-xhci.c:3309:54: note: directive argument in the range [1, 89478486]
  In file included from /usr/include/stdio.h:866,
                   from include/qemu/osdep.h:85,
                   from hw/usb/hcd-xhci.c:22:
  /usr/include/bits/stdio2.h:70:10: note: '__builtin___snprintf_chk' output between 13 and 20 bytes into a destination of size 16
     70 |   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
        |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     71 |        __bos (__s), __fmt, __va_arg_pack ());
        |        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  hw/usb/hcd-xhci.c:3323:54: error: '%d' directive output may be truncated writing between 1 and 8 bytes into a region of size 5 [-Werror=format-truncation=]
   3323 |             snprintf(port->name, sizeof(port->name), "usb3 port #%d", i+1);
        |                                                      ^~~~~~~~~~~~~~~
  hw/usb/hcd-xhci.c:3323:54: note: directive argument in the range [1, 89478486]
  In file included from /usr/include/stdio.h:866,
                   from include/qemu/osdep.h:85,
                   from hw/usb/hcd-xhci.c:22:
  /usr/include/bits/stdio2.h:70:10: note: '__builtin___snprintf_chk' output between 13 and 20 bytes into a destination of size 16
     70 |   return __builtin___snprintf_chk (__s, __n, __USE_FORTIFY_LEVEL - 1,
        |          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     71 |        __bos (__s), __fmt, __va_arg_pack ());
        |        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  cc1: all warnings being treated as errors

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20210118181115.313742-1-philmd@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>