gpu: do not double put device node in zx_drm_probe

for_each_available_child_of_node will get and put the node properly,
the following of_node_put will lead to the double put. So just
remove it.

Signed-off-by: zhong jiang <zhongjiang@huawei.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1534472646-10368-1-git-send-email-zhongjiang@huawei.com