Assuming Steam's data in July 2017 was accurate, this chart outlines the changes over the previous seven months:
Given the success of Ryzen, the 3.46% reduction in systems with AMD processors seems questionable. Steam doesn't share much public information about its survey methodologies, such as how many systems it queries per year or the percentage of laptops and desktop PCs, so we can’t use these numbers as a direct comparison of AMD's penetration into gaming rigs.