Resolve Coverity issue regarding not checking return value

Coverity complains that the call to virPCIDeviceDetach() in
qemuPrepareHostdevPCIDevices() doesn't check status return like
other calls.  Seems this just was lurking until a recent change
to this module resulted in Coverity looking harder and finding
the issue.  Introduced by 'a4efb2e33' when function was called
'pciReAttachDevice()'

Just added a ignore_value() since it doesn't appear to matter
if the call fails since we're on a failure path already.

src/qemu/qemu_hostdev.c

@@ -819,7 +819,8 @@ reattachdevs:
         /* NB: This doesn't actually re-bind to original driver, just
          * unbinds from the stub driver
          */
-        virPCIDeviceReattach(dev, driver->activePciHostdevs, NULL);
+        ignore_value(virPCIDeviceReattach(dev, driver->activePciHostdevs,
+                                          NULL));
     }
 
 cleanup: