clk: imx6sx: fix refcount leak in imx6sx_clocks_init()

The of_find_compatible_node() returns a node pointer with refcount
incremented, but there is the lack of use of the of_node_put() when
done. Add the missing of_node_put() to release the refcount.

Signed-off-by: Yangtao Li <tiny.windzz@gmail.com>
Fixes: d5513568 ("ARM: imx: add clock driver for imx6sx")
Signed-off-by: Stephen Boyd <sboyd@kernel.org>