Fix rotate passwd check logic which will write data into un-allocated
memory.
This fixes [YOCTO #735]
(From OE-Core rev: 4499beb9ef70d207e0d1f60eae77634a77fc44c3)
Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>