powercap/dtpm: Fixup kfree for virtual node

When the node is virtual there is no release function associated which
can free the memory.

Free the memory when no 'ops' exists.

Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20220130210210.549877-3-daniel.lezcano@linaro.org