cpufreq: Fix cpufreq_online() return value on errors

Make cpufreq_online() return negative error codes on all errors that
cause the policy to be destroyed, as appropriate.

Signed-off-by: Wang ShaoBo <bobo.shaobowang@huawei.com>
[ rjw: Subject and changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>