# You don't need find or sed, you can use wildcards as git understands them (doesn't depend on your shell):
git checkout -- "*.xml"

# The quotes will prevent your shell to expand the command to only files in the current directory before its execution.
# You can also disable shell glob expansion (with bash) :

set -f
git checkout -- *.xml

# This, of course, will irremediably erase your changes!\