You can just say:
git diff origin/devel..devel
In any case, I'd advise you create a branch for your work, e.g.
git checkout devel # Make sure we are on the 'devel' branch's tip
git checkout -b mybranch # Create a new branch there
git branch -d devel # Get rid of old 'devel'
git checkout -b devel origin/devel # Recreate 'devel' tracking the original site
Go look for
Git Magic