clk: ti: dra7-atl-clock: Fix of_node reference counting

of_find_node_by_name() will call of_node_put() on the node so we need to
get it first to avoid warnings.
The cfg_node needs to be put after we have finished processing the
properties.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Tested-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>