qemu/9p: Don't ignore error in fid clunk

We use the clunk request to do the actual xattr operation. So don't
ignore the error value for fid clunk.

Security model "none" don't support posix acl. Without this patch
guest won't get EOPNOTSUPP error on setxattr("system.posix_acl_access")

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>