kern-tools: fix patch series to git tree validation

kern-tools: fix patch series to git tree validation

Previous changes to the kern-tools improved functionality to ensure that
as a series is considered, it is checked against the tree to confirm that
all patches are really applied.

There was a bug in the subject based detection, such that the first matching
patch was take, and not the last. This change ensures that we start from
the end of a series, not the start.

(From OE-Core rev: 6357657ec5b5687defaf1acdd94c1cf89aa06541)

Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>