tsnep: Remove useless null check before call of_node_put()

No need to add null check before call of_node_put(), since the
implementation of of_node_put() has done it.

Signed-off-by: Haowen Bai <baihaowen@meizu.com>
Link: https://lore.kernel.org/r/1650509283-26168-1-git-send-email-baihaowen@meizu.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>