ANDROID: PM / OPP: Add missing of_node_put() to power estimation helper

of_dev_pm_get_cpu_power() fails to properly decrement the refcount of
the device_node used to read the CPU capacitance.

Fix this.

Bug: 120440300
Fixes: d326aa36 ("ANDROID: PM / OPP: cpufreq-dt: Move power
estimation function")
Change-Id: I860b00a78710b543c5f3746f3ef35179de22ff01
Signed-off-by: Quentin Perret <quentin.perret@arm.com>