drm/rockchip: fix a couple off by one bugs

The priv->crtc_funcs[] array has ROCKCHIP_MAX_CRTC elements so > should
be >= here.

Fixes: 2048e328

 ('drm: rockchip: Add basic drm driver')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Sean Paul <seanpaul@chromium.org>