plat/arm: css: Sanitize the input to css_validate_power_state
plat/arm: css: Sanitize the input to css_validate_power_state

In the case of the platform max power level being less than the system
power level, make sure to not overrun the array of power states.

This fixes Coverity Scan OVERRUN defect CID 267021.

Change-Id: I52646ab9be2fceeb5c331b5dad7a6267991f4197
Signed-off-by: Nariman Poushin <2f8dfc1642bf854c964b211c0e960f1ed63c75bd@linaro.org>

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware