Fix code indent for the sample code in deepseek-chat.adoc

Signed-off-by: Robby Zhao <robby.zhaox@gmail.com>

spring-ai-docs/src/main/antora/modules/ROOT/pages/api/chat/deepseek-chat.adoc

@@ -201,7 +201,7 @@ public class ChatController {
     }
 
     @GetMapping("/ai/generateStream")
-	public Flux<ChatResponse> generateStream(@RequestParam(value = "message", defaultValue = "Tell me a joke") String message) {
+    public Flux<ChatResponse> generateStream(@RequestParam(value = "message", defaultValue = "Tell me a joke") String message) {
         Prompt prompt = new Prompt(new UserMessage(message));
         return this.chatModel.stream(prompt);
     }