drm: Remove 80-column line in drm_mode_object.c

Break line after NULL to decrease the line size.

Signed-off-by: Shayenne da Luz Moura <shayenneluzmoura@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20181031174424.odljb6obj25wm47d@smtp.gmail.com