ttf-dejavu: fix license warnings

Fix LICENSE value to drop warning messages:
WARNING: ttf-dejavu: No generic license file exists for: Bitstream in any provider
WARNING: ttf-dejavu: No generic license file exists for: Vera in any provider

Signed-off-by: Matthieu Crapet <Matthieu.Crapet@ingenico.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>