package/flare-engine: fix check-package failure

Check-package gives error on flare-engine due to trailing whitespace in
flare-engine.mk comment inserted with commit:
https://git.buildroot.net/buildroot/commit/?id=1203cca1b51eefb4ee236d998ab6ec32bdd087d8



Remove trailing whitespace in flare-engine.mk comment.

Signed-off-by: Giulio Benetti <giulio.benetti@micronovasrl.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>