cpuidle: psci: Fix uninitialized variable in dt_idle_state_present()

cpuidle: psci: Fix uninitialized variable in dt_idle_state_present()

If the first cpu_node = of_cpu_device_node_get() fails then the cleanup.h
code will try to free "state_node" but it hasn't been initialized yet.
Declare the device_nodes where they are initialized to fix this.

Fixes: 5836ebeb4a2b ("cpuidle: psci: Avoid initializing faux device if no DT idle states are present")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://patch.msgid.link/aDVRcfU8O8sez1x7@stanley.mountain
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>