Subzero: Fix a warning (promoted to an error) under NOASSERT=1 build.
Subzero: Fix a warning (promoted to an error) under NOASSERT=1 build.

BUG= none
R=kschimpf@google.com

Review URL: https://codereview.chromium.org/951283002

bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader