Change "balance" to "ondemand" in help info for "xenpm set-cpufreq-cppc"
Fixes: 81ce87fc5e (xen/cpufreq: rename cppc preset name to "XEN_SYSCTL_CPPC_SET_PRESET_ONDEMAND")
Signed-off-by: Penny Zheng <Penny.Zheng@amd.com>
Acked-by: Jan Beulich <jbeulich@suse.com>