Yes, you need to enter the amount that you withdrew from the 401(k) in 2015 and did not roll over to another retirement account. The distribution made in 2015 must be subtracted from the amount of your 2016 contribution and only the remainder is considered for the Retirement Savings Contributions Credit. Apparently your 2015 distribution is larger than the amount you contributed for 2016, so you are not entitled to the tax credit.
