mesa: fix glUniform* when a struct contains a bindless sampler

mesa: fix glUniform* when a struct contains a bindless sampler

Small example from #3271:

layout (bindless_sampler) uniform;
struct SamplerSparse {
  sampler2D tex;
  vec4 size;
  [...]
};
uniform SamplerSparse foo;

'foo' will be marked as bindless but we should only take the assign-as-GLuint64 path for 'tex'.

Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/3271
Fixes: 990c8d15ac3 ("mesa: fix setting uniform variables for bindless samplers/images")
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6730>