nir: inline block_add_pred() a few places

It was being used to initialize function impls and loops, even though
it's really a control flow modification helper. It's pretty trivial, so
just inline it to avoid the dependency.

Signed-off-by: Connor Abbott <connor.w.abbott@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/glsl/nir/nir.c

@@ -267,8 +267,7 @@ nir_function_impl_create(nir_function_overload *overload)
    exec_list_push_tail(&impl->body, &start_block->cf_node.node);
 
    start_block->successors[0] = end_block;
-   block_add_pred(end_block, start_block);
-
+   _mesa_set_add(end_block->predecessors, start_block);
    return impl;
 }
 
@@ -334,7 +333,7 @@ nir_loop_create(void *mem_ctx)
    body->cf_node.parent = &loop->cf_node;
 
    body->successors[0] = body;
-   block_add_pred(body, body);
+   _mesa_set_add(body->predecessors, body);
 
    return loop;
 }