Fixes the following ASAN report:

Direct leak of 128 byte(s) in 8 object(s) allocated from:
    #0 0x7fefce311850 in malloc (/lib64/libasan.so.4+0xde850)
    #1 0x7fefcdd5ef0c in g_malloc ../glib/gmem.c:94
    #2 0x559b976faff0 in create_ahci_io_test /home/elmarco/src/qemu/tests/ahci-test.c:1810

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20180215212552.26997-6-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>