hwspinlock: sprd: Check the return value of clk_prepare_enable()

We must check the return value of clk_prepare_enable() to make sure the
hardware spinlock controller can be enabled successfully, otherwise we
should return error.

Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>