clk: s2mps11: Simplify s2mps11_clk_probe unwind paths

The devm_clk_unregister() in .probe error case is not necessary as it will
be automatically called when probe fails.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>