qemu-img: fix segment fault when the image format is qed

qemu-img: fix segment fault when the image format is qed

[root@f15 qemu]# qemu-img info /home/zwu/work/misc/rh6.img
image: /home/zwu/work/misc/rh6.img
file format: qed
virtual size: 4.0G (4294967296 bytes)
disk size: 1.2G
cluster_size: 65536
Segmentation fault (core dumped)

Today when i were fixing another issue, i found this issue; After simple
investigation, i found that the required clock vm_clock is not created
for qemu tool.

Signed-off-by: Zhi Yong Wu <[email protected]>
Reviewed-by: Stefan Hajnoczi <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>