pci core: assert ENOSPC when add capability

ENOSPC is programming error, assert it for debugging.

cc: Michael S. Tsirkin <mst@redhat.com>
cc: Marcel Apfelbaum <marcel@redhat.com>
cc: Markus Armbruster <armbru@redhat.com>

Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>
Signed-off-by: Cao jin <caoj.fnst@cn.fujitsu.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/pci/pci.c

@@ -2228,10 +2228,8 @@ int pci_add_capability2(PCIDevice *pdev, uint8_t cap_id,
 
     if (!offset) {
         offset = pci_find_space(pdev, size);
-        if (!offset) {
-            error_setg(errp, "out of PCI config space");
-            return -ENOSPC;
-        }
+        /* out of PCI config space is programming error */
+        assert(offset);
     } else {
         /* Verify that capabilities don't overlap.  Note: device assignment
          * depends on this check to verify that the device is not broken.