libc/pathbuffer: fix build warning on tasking

[263/1096] Building C object libs/libc/CMakeFiles/c.dir/misc/lib_pathbuffer.c.obj
ctc W574: ["libs/libc/misc/lib_pathbuffer.c" 144/3] 'return' with an expression in function returning void

Signed-off-by: chao an <anchao@lixiang.com>

libs/libc/misc/lib_pathbuffer.c

@@ -141,6 +141,6 @@ void lib_put_pathbuffer(FAR char *buffer)
   /* Free the buffer if it was dynamically allocated */
 
 #ifdef CONFIG_LIBC_PATHBUFFER_MALLOC
-  return lib_free(buffer);
+  lib_free(buffer);
 #endif
 }