The cpu index was wrongly checked causing it to assert always.
Since this code path is exercised only during TF test "NODE_HW_STAT",
which queries Power state from SCP, this bug was not detected earlier.

Change-Id: Ia25cef4c0aa23ed08092df39134937a2601c21ac
Signed-off-by: Manish Pandey <manish.pandey2@arm.com>