Refactor mmap system call code to follow pintos style in indentation

src/vm/mmap.c

@@ -87,6 +87,7 @@ mmap_unmap (struct mmap_entry *mmap)
       hash_delete (&thread_current ()->pages, &page->elem);
     }
 
+  /* Close the file and free the mmap entry. */
   file_close (mmap->file);
   free (mmap);
 }