Correct constness on input_buffer flush.
Correct constness on input_buffer flush.

gardell/vulkan-cpp-library,google/vulkan-cpp-library,aonorin/vulkan-cpp-library,aonorin/vulkan-cpp-library,google/vulkan-cpp-library,google/vulkan-cpp-library,gardell/vulkan-cpp-library,aonorin/vulkan-cpp-library