lxc: fix logic bug

Detected by Coverity.  We want to increment the size_t counter,
not the pointer to the counter.  Bug present since 5f5c6fde (0.9.5).

* src/lxc/lxc_controller.c (lxcSetupLoopDevices): Use correct
precedence.

src/lxc/lxc_controller.c

@@ -210,7 +210,7 @@ static int lxcSetupLoopDevices(virDomainDefPtr def, size_t *nloopDevs, int **loo
             virReportOOMError();
             goto cleanup;
         }
-        (*loopDevs)[*nloopDevs++] = fd;
+        (*loopDevs)[(*nloopDevs)++] = fd;
     }
 
     VIR_DEBUG("Setup all loop devices");