hw/cxl/cxl-cdat: Fix type of buf in ct3_load_cdat()

hw/cxl/cxl-cdat: Fix type of buf in ct3_load_cdat()

When setting GLIB_VERSION_MAX_ALLOWED to GLIB_VERSION_2_58 or higher
(which we'll certainly do in the not too distant future), glib adds
type safety checks to the g_steal_pointer() macro. This trigger an
error in the ct3_load_cdat() function: The local char *buf variable is
assigned to uint8_t *buf in CDATObject, i.e. a pointer of a different
type. Change the local variable to the same type as buf in CDATObject
to avoid the error.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>