qemuDomainObjPrivateDataClear: Don't leak @migParams

qemuDomainObjPrivateDataClear: Don't leak @migParams

Allocated in qemuMigrationParamsNew() we need to free
priv->job.migParams when no longer needed.

==8061== 234 (192 direct, 42 indirect) bytes in 1 blocks are definitely lost in loss record 112 of 123
==8061==    at 0x4C2CF26: calloc (vg_replace_malloc.c:711)
==8061==    by 0x5325D05: virAlloc (viralloc.c:144)
==8061==    by 0x1984F9: qemuMigrationParamsNew (qemu_migration_params.c:218)
==8061==    by 0x19A352: qemuMigrationParamsParse (qemu_migration_params.c:1185)
==8061==    by 0x1604D8: qemuDomainObjPrivateXMLParseJob (qemu_domain.c:2390)
==8061==    by 0x160AE9: qemuDomainObjPrivateXMLParse (qemu_domain.c:2517)
==8061==    by 0x5419EAE: virDomainObjParseXML (domain_conf.c:20442)
==8061==    by 0x541A25E: virDomainObjParseNode (domain_conf.c:20555)
==8061==    by 0x541A2FC: virDomainObjParseFile (domain_conf.c:20574)
==8061==    by 0x13607D: testCompareStatusXMLToXMLFiles (qemuxml2xmltest.c:75)
==8061==    by 0x14F3E8: virTestRun (testutils.c:180)
==8061==    by 0x14DCD0: mymain (qemuxml2xmltest.c:1200)

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