An earlier patch that introduced the function failed to handle the case
where an image format layout qualifier is not specified, which is allowed
on desktop GL profiles. In these cases, nir_variable's image format is
GL_NONE, and we don't need to print a debug message for those.
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Rob Clark <robdclark@gmail.com>
c2ebc38052