Fixed:
DeprecationWarning: The 'warn' method is deprecated, use 'warning' instead
(Bitbake rev: a3f464d202dafef4538e66c008cdecb7b8709ed1)
Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>