virDomainFSDefFree: Unref private data

virDomainFSDefFree: Unref private data

The privateData object is allocated in virDomainFSDefNew() but
never unref'd.

==119642== 480 bytes in 20 blocks are definitely lost in loss record 656 of 671
==119642==    at 0x4837B86: calloc (vg_replace_malloc.c:762)
==119642==    by 0x57806A0: g_malloc0 (in /usr/lib64/libglib-2.0.so.0.6000.7)
==119642==    by 0x4AE7392: virAllocVar (viralloc.c:331)
==119642==    by 0x4B64395: virObjectNew (virobject.c:241)
==119642==    by 0x48F1464: qemuDomainFSPrivateNew (qemu_domain.c:1427)
==119642==    by 0x4BBF004: virDomainFSDefNew (domain_conf.c:2307)
==119642==    by 0x4BD859A: virDomainFSDefParseXML (domain_conf.c:11217)
==119642==    by 0x4BF9DD1: virDomainDefParseXML (domain_conf.c:21179)
==119642==    by 0x4BFCD5B: virDomainDefParseNode (domain_conf.c:21943)
==119642==    by 0x4BFCC36: virDomainDefParse (domain_conf.c:21901)
==119642==    by 0x4BFCCCB: virDomainDefParseFile (domain_conf.c:21924)
==119642==    by 0x114A9D: testCompareXMLToArgv (qemuxml2argvtest.c:452)

Fixes: 5120577ed79f89e172e3deed534fa9b585f4701f
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>