git show-ref looks at the _remote_ ref called HEAD, which is fine when it
matches the local HEAD but problematic when you're iterating a series of
commits.
Use rev-parse to resolve the local name to a proper hash.
(From OE-Core rev: 3c04747b681cf6090ba9c77752f6c2f304dbbe17)
Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
28324600cb