HSI: omap_ssi: Fix refcount leak in ssi_probe

When returning or breaking early from a
for_each_available_child_of_node() loop, we need to explicitly call
of_node_put() on the child node to possibly release the node.

Fixes: b209e047

 ("HSI: Introduce OMAP SSI driver")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>