[KWrite] Correct error message

Summary: When trying to run KWrite with sudo the warning talks about Kate

Test Plan:
Run KWrite with sudo: Error message says KWrite
Run Kate with sudo: Error message says Kate

Reviewers: Kate, dhaumann

Reviewed By: Kate, dhaumann

Subscribers: dhaumann, kwrite-devel

Tags: Kate

Differential Revision: https://phabricator.kde.org/D17646