dEQP-VK.geometry: use proper layout for sampling the image

dEQP-VK.geometry: use proper layout for sampling the image

While 'GENERAL' layout is acceptable layout for sampling image, the barrier in
geometry\vktGeometryBasicGeometryShaderTests.cpp:235
transitions the image to `SHADER_READ_ONLY_OPTIMAL` layout.

Both layout must much, otherwise the behavior is undefined.

Affects:
dEQP-VK.geometry.basic.output_vary_by_texture_instancing
dEQP-VK.geometry.basic.output_vary_by_texture

Components: Vulkan

VK-GL-CTS issue: 648

Change-Id: I2b947a150173f0a060cfbf851d117ef91097c1d8