drm: "kobject_init/kobject_add" -> "kobject_init_and_add".

Replace sequential calls to kobject_init() and kobject_add() with the
combo wrapper kobject_init_and_add(), which provides the same
semantics.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Dave Airlie <airlied@redhat.com>