target: hax: replace g_malloc with g_new0

target: hax: replace g_malloc with g_new0

And also the g_malloc doesn't need check return value,
remove it.

Cc: qemu-trivial@nongnu.org
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Li Qiang <liq3ea@gmail.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <1543226179-5135-1-git-send-email-liq3ea@gmail.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>