Fix statement with no effect in linuxkpi's xarray.h

[dim]

Summary

When compiling the kernel with gcc 14, errors similar to the following
are emitted:

sys/dev/cxgbe/iw_cxgbe/ev.c: In function 'c4iw_ev_handler':
sys/compat/linuxkpi/common/include/linux/xarray.h:132:23: error: statement with no effect [-Werror=unused-value]
  132 |                 flags == 0; \
sys/dev/cxgbe/iw_cxgbe/ev.c:274:17: note: in expansion of macro 'xa_unlock_irqrestore'
  274 |                 xa_unlock_irqrestore(&dev->cqs, flag);
      |                 ^~~~~~~~~~~~~~~~~~~~
sys/compat/linuxkpi/common/include/linux/xarray.h:132:23: error: statement with no effect [-Werror=unused-value]
  132 |                 flags == 0; \
sys/dev/cxgbe/iw_cxgbe/ev.c:283:17: note: in expansion of macro 'xa_unlock_irqrestore'
  283 |                 xa_unlock_irqrestore(&dev->cqs, flag);
      |                 ^~~~~~~~~~~~~~~~~~~~

It looks like the intent of the "flags == 0" statement was to make the
'flags' macro argument not unused, but it still results in a warning.
Use the construct "(void)flags" instead.

[bz]

sys/compat/linuxkpi/common/include/linux/xarray.h

132

If you wanted to keep it in sync with the spinlock implementation it'd be reverse order

(void)flags;
xa_unlock((xa));

but who cares in this case.