Search for Higgs Boson Pair Production in the Four <mml:math xmlns:mml='http://www.w3.org/1998/Math/MathML' display='inline'><mml:mi>b</mml:mi></mml:math> Quark Final State in Proton-Proton Collisions at <mml:math xmlns:mml='http://www.w3.org/1998/Ma