powerpc/powermac/low_i2c: Add missing of_node_put() in kw_i2c_probe()

Call of_node_put() for the reference 'parent' returned by
of_get_parent() which has increased the refcount.

Signed-off-by: Liang He <windhl@126.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220716070758.539434-1-windhl@126.com