qemu: conf: Don't leak 'namespaces' temporary variable while parsing config

qemu: conf: Don't leak 'namespaces' temporary variable while parsing config

==20406== 8 bytes in 1 blocks are definitely lost in loss record 24 of 1,059
==20406==    at 0x4C2CF55: calloc (vg_replace_malloc.c:711)
==20406==    by 0x54BF530: virAllocN (viralloc.c:191)
==20406==    by 0x54D37C4: virConfGetValueStringList (virconf.c:1001)
==20406==    by 0x144E4E8E: virQEMUDriverConfigLoadFile (qemu_conf.c:835)
==20406==    by 0x1452A744: qemuStateInitialize (qemu_driver.c:664)
==20406==    by 0x55DB585: virStateInitialize (libvirt.c:770)
==20406==    by 0x124570: daemonRunStateInit (libvirtd.c:881)
==20406==    by 0x5532990: virThreadHelper (virthread.c:206)
==20406==    by 0x8C82493: start_thread (in /lib64/libpthread-2.24.so)
==20406==    by 0x8F7FA1E: clone (in /lib64/libc-2.24.so)