Fix Coverity #343017, Missing unlock
Fix Coverity #343017, Missing unlock

All other returns from this function unlock the responses_lock, so we
also should release the lock in this case.

Change-Id: Ie2cfa8755723fed79e809f9480190d11f373a217
Signed-off-by: Justin Chadwell <23868ac6bb803cbca62577fbb15c1a832c6e5215@arm.com>

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