qemu: fix blkio memory leak on failure

Leak detected by Coverity, and introduced in commit 93ab5859.
Reported by Alex Jia.

* src/qemu/qemu_driver.c (qemuDomainSetBlkioParameters): Free
devices array on error.

src/qemu/qemu_driver.c

@@ -6012,11 +6012,8 @@ static int qemuDomainSetBlkioParameters(virDomainPtr dom,
                         break;
                     }
                 }
-                if (j != ndevices) {
-                    ret = -1;
-                    continue;
-                }
-                if (qemuDomainMergeDeviceWeights(&vm->def->blkio.devices,
+                if (j != ndevices ||
+                    qemuDomainMergeDeviceWeights(&vm->def->blkio.devices,
                                                  &vm->def->blkio.ndevices,
                                                  devices, ndevices) < 0)
                     ret = -1;