in virDomainFSInfoFree(), don't free the virDomainFSInfo data.

==10670== 80 bytes in 2 blocks are definitely lost in loss record 576 of 793
==10670==    at 0x4A06BC3: calloc (vg_replace_malloc.c:618)
==10670==    by 0x509DEBD: virAlloc (viralloc.c:144)
==10670==    by 0x19FBD558: qemuAgentGetFSInfo (qemu_agent.c:1837)
==10670==    by 0x1A03CF91: qemuDomainGetFSInfo (qemu_driver.c:19238)
Signed-off-by: NChen Fan <chen.fan.fnst@cn.fujitsu.com>
(cherry picked from commit f276b36d)