One section of the code is enforcing lowercase overrides, the other
is allowing numeric characters. We should be consistent with one or
the other.
(Bitbake rev: df5b3b841fd8d6a652d643e9ae2bba09d60043e0)
Signed-off-by: 张忠山 <zzs213@126.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>