st/mesa: remove !obj checking in _mesa_get_bufferobj_reference when it's useless

There is at least one case in a future commit where the compiler can't do
this automatically.

Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/27587>

src/mesa/main/bufferobj.h

@@ -36,12 +36,10 @@
  * Internal functions
  */
 
-static inline struct pipe_resource *
+static ALWAYS_INLINE struct pipe_resource *
 _mesa_get_bufferobj_reference(struct gl_context *ctx, struct gl_buffer_object *obj)
 {
-   if (unlikely(!obj))
-      return NULL;
-
+   assert(obj);
    struct pipe_resource *buffer = obj->buffer;
 
    /* Only one context is using the fast path. All other contexts must use

src/mesa/state_tracker/st_atom_constbuf.c

@@ -282,7 +282,12 @@ st_bind_ubos(struct st_context *st, struct gl_program *prog,
       binding =
          &st->ctx->UniformBufferBindings[prog->sh.UniformBlocks[i]->Binding];
 
-      cb.buffer = _mesa_get_bufferobj_reference(st->ctx, binding->BufferObject);
+      if (binding->BufferObject) {
+         cb.buffer = _mesa_get_bufferobj_reference(st->ctx,
+                                                   binding->BufferObject);
+      } else {
+         cb.buffer = NULL;
+      }
 
       if (cb.buffer) {
          cb.buffer_offset = binding->Offset;