mesa: Fix the BindSampler unit limit.

I'm not sure about this one. The current code actually follows the spec, but
considering the spec is supposed to be written against GL 3.2 I'd say the spec
is broken. I filled out a spec feedback form over a month ago, but either the
form is broken, or nobody cares.

Signed-off-by: Henri Verbeet <hverbeet@gmail.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/mesa/main/samplerobj.c

@@ -251,7 +251,7 @@ _mesa_BindSampler(GLuint unit, GLuint sampler)
    struct gl_sampler_object *sampObj;
    GET_CURRENT_CONTEXT(ctx);
 
-   if (unit >= ctx->Const.MaxTextureImageUnits) {
+   if (unit >= ctx->Const.MaxCombinedTextureImageUnits) {
       _mesa_error(ctx, GL_INVALID_VALUE, "glBindSampler(unit %u)", unit);
       return;
    }