compositor-drm: Add missing newline to debug print

The 'created new mode blob' print was missing a newline, unlike all the
others.

Signed-off-by: Daniel Stone <daniels@collabora.com>
2 jobs from drm-add-missing-newline-to-debug in 5 minutes and 20 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Build
passed #121120
build-native-autotools

00:05:20

passed #121121
build-native-meson

00:02:07