clk: s2mps11: Fix possible NULL pointer dereference

If parent device does not have of_node set the s2mps11_clk_parse_dt()
returned NULL. This NULL was later passed to of_clk_add_provider() which
dereferenced it in pr_debug() call.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>