virsh: don't leak @cpumap in virshVcpuPinQuery

virsh: don't leak @cpumap in virshVcpuPinQuery

==18591== 16 bytes in 1 blocks are definitely lost in loss record 41 of 183
==18591==    at 0x4C2B934: calloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
==18591==    by 0x54EBB1C: virAllocN (viralloc.c:191)
==18591==    by 0x1628CA: _vshMalloc (vsh.c:136)
==18591==    by 0x1344C4: virshVcpuPinQuery (virsh-domain.c:6603)
==18591==    by 0x1344C4: cmdVcpuPin (virsh-domain.c:6707)
==18591==    by 0x1631BF: vshCommandRun (vsh.c:1312)
==18591==    by 0x12DBB1: main (virsh.c:961)