[example] Fix formatting in documentation comments for hello_world function in hello.c and hello.h

Author: BernardXiong

tools/hello/hello.c

@@ -13,7 +13,7 @@
 
 /**
  * @brief Hello world function implementation
- * 
+ *
  * This function prints "Hello World!" to the console using rt_kprintf
  */
 void hello_world(void)

tools/hello/hello.h

@@ -17,7 +17,7 @@ extern "C" {
 
 /**
  * @brief Hello world function
- * 
+ *
  * This function prints "Hello World!" to the console
  */
 void hello_world(void);