We are using the hlsl_ir_var.is_uniform flag to indicate when an object
is a uniform copy created from a variable with the HLSL_STORAGE_UNIFORM
modifier.
We should be checking for this instead of the HLSL_STORAGE_UNIFORM flag
which is also set to 1 for the original variables, and there should be
no reason to use this flag instead of "is_uniform" after the uniform
copies and combined/separated samplers are created.