drm/gem: Remove trailing whitespace

Remove two trailing spaces.
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171026165731.5793-4-noralf@tronnes.org