basename: return path address instead of "/" when path="/"

Signed-off-by: guohao15 <guohao15@xiaomi.com>

libs/libc/libgen/lib_basename.c

@@ -83,7 +83,7 @@ FAR char *basename(FAR char *path)
         }
       else
         {
-          return "/";
+          return path;
         }
     }