hw/pci-bridge/cxl_upstream.c: Use g_new0() in build_cdat_table()

hw/pci-bridge/cxl_upstream.c: Use g_new0() in build_cdat_table()

In build_cdat_table() we do:
 *cdat_table = g_malloc0(sizeof(*cdat_table) * CXL_USP_CDAT_NUM_ENTRIES);
This is wrong because:
 - cdat_table has type CDATSubHeader ***
 - so *cdat_table has type CDATSubHeader **
 - so the array we're allocating here should be items of type CDATSubHeader *
 - but we pass sizeof(*cdat_table), which is sizeof(CDATSubHeader **),
   implying that we're allocating an array of CDATSubHeader **

It happens that sizeof(CDATSubHeader **) == sizeof(CDATSubHeader *)
so nothing blows up, but this should be sizeof(**cdat_table).

Avoid this excessively hard-to-understand code by using
g_new0() instead, which will do the type checking for us.
While we're here, we can drop the useless check against failure,
as g_malloc0() and g_new0() never fail.

This fixes Coverity issue CID 1508120.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20230718101327.1111374-1-peter.maydell@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>