virsh-domain: Fix memleak in cmdCPUBaseline

virsh-domain: Fix memleak in cmdCPUBaseline

https://bugzilla.redhat.com/show_bug.cgi?id=997765

==1349431== 8 bytes in 1 blocks are definitely lost in loss record 11 of 760
==1349431==    at 0x4C2A554: calloc (vg_replace_malloc.c:593)
==1349431==    by 0x4E9AA3E: virAllocN (in /usr/lib64/libvirt.so.0.1001.1)
==1349431==    by 0x4EF28C4: virXPathNodeSet (in /usr/lib64/libvirt.so.0.1001.1)
==1349431==    by 0x130B83: cmdCPUBaseline (in /usr/bin/virsh)
==1349431==    by 0x12C608: vshCommandRun (in /usr/bin/virsh)
==1349431==    by 0x12889A: main (in /usr/bin/virsh)