devtool: modify: get correct initial revision from previously extracted source tree
If you point devtool modify to a source tree previously created by
devtool modify or devtool extract, then we need to try to pick up the
correct initial revision so that devtool update-recipe knows where to
start looking for commits that match up with patches in the recipe.
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
