Fix a memory leak

The below patch fixes the following memory leak.

==20624== 24 bytes in 2 blocks are definitely lost in loss record 532 of 1,867
==20624==    at 0x4A05E46: malloc (vg_replace_malloc.c:195)
==20624==    by 0x38EC27FC01: strdup (strdup.c:43)
==20624==    by 0x4EB6BA3: virDomainChrSourceDefCopy (domain_conf.c:1122)
==20624==    by 0x495D76: qemuProcessFindCharDevicePTYs (qemu_process.c:1497)
==20624==    by 0x498321: qemuProcessWaitForMonitor (qemu_process.c:1258)
==20624==    by 0x49B5F9: qemuProcessStart (qemu_process.c:3652)
==20624==    by 0x468B5C: qemuDomainObjStart (qemu_driver.c:4753)
==20624==    by 0x469171: qemuDomainStartWithFlags (qemu_driver.c:4810)
==20624==    by 0x4F21735: virDomainCreate (libvirt.c:8153)
==20624==    by 0x4302BF: remoteDispatchDomainCreateHelper (remote_dispatch.h:852)
==20624==    by 0x4F72C14: virNetServerProgramDispatch (virnetserverprogram.c:416)
==20624==    by 0x4F6D690: virNetServerHandleJob (virnetserver.c:164)
==20624==    by 0x4E8F43D: virThreadPoolWorker (threadpool.c:144)
==20624==    by 0x4E8EAB5: virThreadHelper (threads-pthread.c:161)
==20624==    by 0x38EC606CCA: start_thread (pthread_create.c:301)
==20624==    by 0x38EC2E0C2C: clone (clone.S:115)

src/conf/domain_conf.c

@@ -1173,6 +1173,8 @@ virDomainChrSourceDefCopy(virDomainChrSourceDefPtr dest,
         break;
     }
 
+    dest->type = src->type;
+
     return 0;
 }