drm/debugfs: remove redundant info from gem_names

It's a relic of "drm: Convert proc files to seq_file and introduce debugfs",
which wrongly converted DRM_INFO + sprintf to 2 seq_printfs.

Signed-off-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Cc: Ben Gamari <bgamari@gmail.com>
Cc: Eric Anholt <eric@anholt.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>