tcg: Silent -Wmissing-field-initializers warning

tcg: Silent -Wmissing-field-initializers warning

Silent when compiling with -Wextra:

  tcg/i386/tcg-target.opc.h:34:1: warning: missing field 'args_ct' initializer [-Wmissing-field-initializers]
  DEF(x86_punpckl_vec, 1, 2, 0, IMPLVEC)
  ^
  ../tcg/tcg-common.c:30:66: note: expanded from macro 'DEF'
         { #s, oargs, iargs, cargs, iargs + oargs + cargs, flags },
                                                                 ^

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20221220143532.24958-2-philmd@linaro.org>