vk/vec4: Use the right constant for offset into a UBO
vk/vec4: Use the right constant for offset into a UBO

We were using constant 0, which is the set.

Signed-off-by: Kristian Høgsberg Kristensen <4b441a45a1cdbce08ca0aaabb01d554a77184d64@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler