ch7006: correctly handling failed allocation

Since drm_property_create_range can be failed in memory pressure,
it needs to be checked and return -ENOMEM.

Signed-off-by: Insu Yun <wuninsu@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1454025276-13465-1-git-send-email-wuninsu@gmail.com