pci: Fix the wrong assertion.

pci_add_capability returns a strictly positive value on success,
correct asserts.

Cc: dmitry@daynix.com
Cc: jasowang@redhat.com
Cc: kraxel@redhat.com
Cc: alex.williamson@redhat.com
Cc: armbru@redhat.com
Cc: marcel@redhat.com
Signed-off-by: Mao Zhongyi <maozy.fnst@cn.fujitsu.com>
Reviewed-by: Marcel Apfelbaum <marcel@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/net/e1000e.c

@@ -374,7 +374,7 @@ e1000e_add_pm_capability(PCIDevice *pdev, uint8_t offset, uint16_t pmc)
 {
     int ret = pci_add_capability(pdev, PCI_CAP_ID_PM, offset, PCI_PM_SIZEOF);
 
-    if (ret >= 0) {
+    if (ret > 0) {
         pci_set_word(pdev->config + offset + PCI_PM_PMC,
                      PCI_PM_CAP_VER_1_1 |
                      pmc);

hw/net/eepro100.c

@@ -571,7 +571,7 @@ static void e100_pci_reset(EEPRO100State * s)
         int cfg_offset = 0xdc;
         int r = pci_add_capability(&s->dev, PCI_CAP_ID_PM,
                                    cfg_offset, PCI_PM_SIZEOF);
-        assert(r >= 0);
+        assert(r > 0);
         pci_set_word(pci_conf + cfg_offset + PCI_PM_PMC, 0x7e21);
 #if 0 /* TODO: replace dummy code for power management emulation. */
         /* TODO: Power Management Control / Status. */

hw/usb/hcd-xhci.c

@@ -3419,7 +3419,7 @@ static void usb_xhci_realize(struct PCIDevice *dev, Error **errp)
     if (pci_bus_is_express(dev->bus) ||
         xhci_get_flag(xhci, XHCI_FLAG_FORCE_PCIE_ENDCAP)) {
         ret = pcie_endpoint_cap_init(dev, 0xa0);
-        assert(ret >= 0);
+        assert(ret > 0);
     }
 
     if (xhci->msix != ON_OFF_AUTO_OFF) {

hw/vfio/pci.c

@@ -1744,7 +1744,7 @@ static int vfio_setup_pcie_cap(VFIOPCIDevice *vdev, int pos, uint8_t size,
     }
 
     pos = pci_add_capability(&vdev->pdev, PCI_CAP_ID_EXP, pos, size);
-    if (pos >= 0) {
+    if (pos > 0) {
         vdev->pdev.exp.exp_cap = pos;
     }